James, I think you are looking for a Herbrand No. 188 brake tool. Go to ebay and you will see several examples for sale. This is one tool you need if you are going to work on Huck brakes which Chevy used on their trucks from the 30s until 1950.

Kent

1937 Chevy 1/2 ton
1942 Chevy 1/2 ton
1947 Diamond T Model 509
1951 Chevy 1/2 ton
1950 Chevy COE Model 5700 ~ "Barney" ~ And more pix