Ed is right. Let me clarify my comment. The axle housing will fit either single or two speed differential carriers. The carrier housing itself is different for the two types. He is also correct about "slow and slower".
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