340 Piston to valve clearance w/RHS heads
.035 on the quench should be fine. .080 on the intakes and .100 on the exhausts. Do the mock up with clay to be sure.
Yeah I believe the Chevy guys run it that close too. It would just stink thou to have a great running engine for awhile and then one day showing off on the freeway to your GF--or better yet--your GF winding out the engine in 2 gear on the freeway and bang, boom and white smoke goes pouring out the rear while the engine gets weak while your foot is still down on the gas--I blew a head gasket once like that.
I wasn't thinking of making the heads open chamber, just grinding .015 in for extra space. Or take it off the pistons. Most pistons should have valve reliefs already in. Maybe it be open but i can't see the harm .015 would do
So far my kb 340 hypers been holding up, only 2,500 miles on the engine but hard miles. I stayed on the 6,500 rev limiter for a good 10 seconds last summer. All was fine. Not a wiff of smoke either in back. Hyper pistons run tight and seal great. If you don't ping the engine--by too much timing, too lean, it should work fine.
I was all against hyper's too but for $250 for a new set at Summit it got my engine going and I now think its going to last. I'm getting taller tires for sure and maybe stick my 3.21 gears back in. If $4 a gallon gas shows up this spring, yuk. I'm going for mileage over performance