you want the 8" front diff?
...ok.
I'd scrap the 80 front end. on a 40 series.
option A
Use 1968-1984 40 series OR 1984-1990 70 series (move front spring perch, axles are same width). Install 9.5" elocker or whatever w/ 30 spline longs
option B
for wider track, use J60/61/62 front axle but please note, the right side spring perch is an issue spring under.
I'd re ask this question on the 40 section or hard core and get guys like Poser to chime in.
the 9.5" is certainly stronger than the 8" reverse cut any day of the week (strong, multi year evidence from canadian mine truck use where ratio is 1:6 in favor of the 9.5"- rear.