Single leg to a Posi unit ?

[ck5566]

I have a 68 C10 coils all 4 corners, with that said I would like to know if or how easy it is to turn a single leg rear end mine (3.73) into a Posi rear third member unit. I am not real found of my 3.73's would like to go with 3.42's. The eng is a (for now) 305 with a 700R4. I would like to go 3.07's for when the 350 gets "built" but for now with the 305eng I think the 3.42's will get along better with each other (305/700R4/3.42) So what do you all think. thanks in advance