I haven't played around with a Chevy in years, I figure Mopar well the 340 anyway, had the open chamber, and they used the piston dome to change CR. Actually pretty convenient I think. Mopar engineers were some of the best IMO. Right now I have an E6 headed Ford Mustang GT engine that I want to put E7s on but I hear tell with no valve reliefs in the 86 Piston that that is a no, no. However some say it can be done. Thing is i have the parts LOL! but the Fox body runs pretty dern good I hate to mess with it too much, but I may just start taking it down the engine needs a reseal of gaskets anyway. Throw on th eE& heads with the 87 and up intalke and voila upgrade done for an extra 30 HP so they say...