Ron - Thanks for the reply, new member here....I want to swap out the 4.57's in my 1948 3600 with a 4.10 unit from a 68-72 C or K20, as described in the article:

https://www.stovebolt.com/techtips/axles/1%20Ton%20Upgrade/

The article states the donor vehicles (3/4 tons) will have an HO52 gear set, but you say I need an HO72 set, can you explain - Thanks