Well humble opinion here but f you must use a chevy, (And dont get me wrong I still love a SBC just not as much as my ramblers..) find a 400 small block.. absolutely the best bang for the buck.. and dont let people tell ya they crack if they overheat.. thats a load.. they have steam holes in the head/block and all the "experts" decided they would crack..so after 50 jillion of em and no trouble .. not so much..
But with the 400 when you get the "bigger faster bug" you order the 383 kit from jegs and build a mail order stroker..
(the only real advantage the SBC has over the AMC.. is I can go to almost any swap meet and buy any manifold/crank cam whosits ever created for the dang thing for 25 bucks.. cause there are so many of them.. Sigh..oh w)ell..