Don,t worry about the block..they are all the same. The heads are what you should look at. The most desirable are the D0VE heads, that D as inthe 70's; Zero as in 1970; V as in valve and E as in Engine. They are the Pre Emission heads and have HUGE ports and small Chambers and......Screw in Rocker shafts!!!!! However any year will make a TON of touque with a Cam, Carb, Manifold & Exhaust!