There is so little room back there I'm not sure it's worth the trouble. Two saddle tanks will give you pretty decent range and everything you need to install the reserve tank are off-the-shelf parts.
Four wheel drive allows you to get stuck
in places even more inaccessible.
62 88 Regular
67 109 6cyl NADA x2
74 Lightweight - The Antichrist
95 DI 5-speed
95 D90 5-speed
97 D1 Automatic