Just to add to this thread,... ECE (
www.earlyclassic.com) sells a direct BOLT-ON spindle that will convert 8-lug trucks to 5-lug (or 6-lug) suspension.
No need to change anything other than the spindle, rotor, and caliper.
I have a set I bought years ago, waiting for the right 3/4-ton truck to come along.
These make the swap super easy.