Rear End

Well, I say use an 8 1/4. Sure an 8 3/4 or D60 would be pretty sweet and it's unlikely that you'd ever 'splode it on accident but you DO NOT need that for a little 318. An 8 1/4 can be had for pretty cheap, will stand up to a 318 pretty well, and it'll bolt right in if you find an A Body unit (check the for sale ads here, they pop up sometimes). If you want disk brakes then try to get an 8 1/4 from a Cherokee. A sure grip and good gears should be easy to come by for an 8 1/4 too. You'll also get more power to the wheels with a smaller rear end because it takes less power to turn it.

I think for this build an 8 1/4 is the way to go. FWIW my 8 1/4 has racked up about 300k miles and has stood up to a 225, 318, and 340 with no issues at all.