Differential swap out options

[Montierth]

I currently have a 1970 GMC with leaf springs, 5 lug, disc brakes, non posi, 12 bolt differential with 3.08 gearing. I am interested in having a 3.73 gearing with posi/limited slip and keeping the 5 lug and disc brakes. I have looked into different options and seems like easiest would be to find a used differential that is already 3.73 and posi. Also, in the future I would like to convert to trailing arms. I have read that somewhere around 1970 the GMCs differential was a little different size than the Chevys?

My question is what would be a simple bolt in? Are there certain years that work better?

I found a 1998 10 bolt 3.73 posi differential someone is selling but I would have to buy 5 lug axles. Not sure though if it would fit.