Frank Phillips, a park maintenance employee whose workmanship and cooperativeness had impressed the installation crew at Custer Battlefield, transferred to the laboratory in July and took on much of the exhibit case and panel construction. After assuming supervisory responsibility in 1964, he proved a hard taskmaster and supported changing design trends that deemphasized concern for exhibit maintenance and specimen protection. Diligent, practical, resourceful, and accurate, he remained with the laboratory until retiring in the mid-1970s. In August came Dan Feaser, who served as a skilled exhibit artist until promoted to the history planning team, and Arlie P. O'Meara, who for the rest of his career operated the spray booth-a necessary task requiring a special kind of reliability along with a good eye and steady hand. In October John A. Segeren was hired as a model maker. He transferred to the western laboratory in September 1958 and returned when it closed, becoming most active as a wood carver. Two more artists engaged in November rounded out the preparation staff: Richard H. Jansen, a mature, Wisconsin-trained painter, and Ray Price.

Only a few later changes occurred in the laboratory's production crew during Mission 66. In June 1958 Arlton C. Murray, an experienced preparator, was assigned from other duties to work on exhibits. Kenneth Dreyer replaced his father as model maker in July 1960. During summer vacations earlier in the program a high school shop teacher, Clair H. Younkin, provided valuable temporary help.

Also essential to the task was increased curatorial support. Mission 66 museums, like their predecessors, each had a story to tell and set out to exhibit the specimens and graphics that would tell it most effectively. The exhibit plan generated a want list to accomplish this. Whether or not the objects needed were already in the park collection had little bearing on their selection. If they were not, Museum Branch curators faced the problem of finding and acquiring them. Efficient exhibit production demanded that the specimens be in the laboratory on schedule, imposing a continual succession of deadlines.

To carry the main burden of search and acquisition the branch hired a new curator in July 1956. Joseph Fred Winkler, a geographer well recommended by his colleagues at the National Archives, combined skill in evaluating and employing reference resources with systematic, tenacious application. When one plan called for a specimen of the extinct passenger pigeon, for example, he obtained a fine mount on time and without fuss. Other staff curators assisted when they could, but Winkler bore the brunt of supplying the preparators with the specimens for exhibition. In July 1956 also Laurence Cone relinquished his duties as an exhibits construction specialist to assist with the curatorial workload. Besides helping with acquisitions, he acted as laboratory photographer and organized the slide files until departing in August 1957 to become curator of the Southern Plains Indian Museum. When the forthcoming Civil War Centennial created a special need for an expert on the war and its material culture, Lee A. Wallace transferred in December 1957 from his position as park historian at Chickamauga and Chattanooga National Military Park to the Museum Branch as exhibit research historian. He provided a continual flow of factual and pictorial data to meet innumerable exhibit needs during the centennial program.

Tempo S did not have vacant rooms suitable for shop use when the need to expand arose. In the summer of 1957 the General Services Administration rented the Park Service a second floor area in another temporary building across Independence Avenue for a laboratory annex. A more convenient location, the rear portion of a wing in Tempo S adjacent to the main laboratory, soon replaced it. GSA also agreed to air condition the laboratory space in Tempo S, completing the installation in June 1958. Although the system could not provide the stable conditions now recommended for museum environments, it greatly facilitated exhibit production during Washington's muggy summers. The Museum Branch later expanded into three front offices as well and borrowed vacant rooms on occasion to serve special needs.

It became apparent at the outset that museum development under Mission 66 would justify reestablishing the Western Museum Laboratory. Besides boosting exhibit production, a laboratory in the West would reduce the costly and hazardous transcontinental shipment of specimens and exhibits. Museum staff could also work much more closely with architects in the Western Office of Design and Construction and with many of the client parks. Setting up and managing the new facility would require someone with broadly based museum experience not easily obtained within the Park Service. The job would demand strong leadership yet willing support of the Service's established museum standards and curatorial policies.

The branch had by chance hired a number of able employees educated or trained in Wisconsin, including Floyd LaFayette and Harold Peterson. They urged the selection of John Jenkins, whom they knew and respected as chief curator of the Wisconsin State Historical Society. Jenkins responded with interest to a March 1956 letter that referred primarily to work on the western planning team with only a suggestion of larger prospects. From this start the Museum Branch secured the establishment of two positions, to be filled consecutively. The first permitted Jenkins' appointment as designer on the exhibit planning team in San Francisco while he also laid the groundwork for the projected laboratory. He took up these duties in October 1956. His advancement to the second position as chief of the Western Museum Laboratory followed in September 1957.

The laboratory was still far from a functioning reality. The Service proposed to house it in the old United States Mint, conveniently located in downtown San Francisco. This massive and somewhat derelict structure had briefly provided the last home for the prewar laboratory. Now it was the focus of controversy between preservationists who wanted to save the building and developers who hoped to demolish it. Locating the laboratory in the Old Mint gave the preservationists a toehold, but its fate remained unsure throughout this occupancy.

GSA assigned basement space in the building for laboratory use on September 28, 1957. Assistant Regional Director Herbert Maier, who thirty years before had so ably designed and supervised construction of park museums for Yosemite and Yellowstone, helped expedite preparation of the space. Work got underway to adapt the old vaults and narrow corridors for laboratory use in January 1958, with the Service footing the bill. Jenkins did not wait for the contractor to finish. On March 17 he started moving in and setting up equipment, and exhibit production began in earnest a week later.