My 66 also had the 8.875 GM (12-bolt TRUCK) rear end, which was also used right through until (iirc) 1981. They're fairly stout, and also an easy swap.
Be sure to grab the 11-5/32" x 2-3/4" rear brake assy's as well.
If you go with a mid-70's 4x4 as the "donor", it will have the same 6-bolt pattern as your 63, retaining a somewhat "stock" appearance.
CPP or Classic Industries have the 6-bolt rotors for the front to match the spindles and calipers from your "upgraded" cross-member.
I love this aspect of the swap. ALL of the brake parts as well as ALL of the front steering and suspension on my truck are all 1976 C10 / K10 pieces (except the rotors of course)
NAPA part numbers for everything are in my journal.