I'm debating the same thing. Although a Dana 18 won't require a differential swap. I am really debating this because the Quadra Trac is a commitment. If you want to keep it you have to stick with it or it will cost you.
I will also lose my dual tank set up if I have to use a rear centered diff
It's already a tight fit
Wag Rebuilt 360, 260H, 727, Locked 44, AMC 20, 208, 31" M/T's, 4" Rustys, 2.5" Duals. SOON:SOA SF, 496, T400, Doubler, D60's, 37" M/T's <-TOY
Cherokee Rebuilt 360, 2" Duals, mostly stock. SOON: Hot Street 401, 4'' Rustys, 33" BFG A/T's maybe a T-case to get rid of Q-Track <-TOW RIG