Shrugod the questions you have to ask yourself
is do I have to conform to EPA regs. If you do I would use a pre "74" block. Also during the 80's alot of the manufacters were looking for ways to save money on production that ment using less material I cant atest that the "86" is one of these but I know the 70's blocks are not. Are they stronger or better? Dont know but I haven't had any problems out of the pre "74's. Of you want to bullet proof that go with the dart block ads 2600 to the build but if its going in your dream car what the heck. 4.125bore 4.000 stroke 6.200 rods JE forged pistons AFR 205 heads Victor Jr intake 825 Mity Demon .600 lift cam will net you around 575-600HP&over 550ft.lbs torque.This might help go to
www.perfeng.cc see what you need. Good Luck on your build take your time do it right the first time.