Shaft lengths are almost treading towards a personal question…
As mentioned above…it depends on your tcase…BUT..I would like to add that it also depends you’re your transmission.
On my 78 K10, I went from the original TH350/NP203 to a TH350/NP205 combo. That cost me lengthening the rear shaft and shortening the front as well as changing the front shaft all together to mate to the 205. Then when I went from the TH350/NP205 to a SM465 manual/NP205 combo back in 1999, I had to lengthen the rear and shorten the front…..If I rember right.