340 Piston to valve clearance w/RHS heads

Yes, that's definitely good advice. Before I took it apart, I measured the #1 and #5 pistons using a dial indicator with its 1.824 compression height cast pistons. With piston rock the worst measurement I could get anywhere was +0.002". The L2316F's are 1.840 compression height so that's where I was getting the general idea from.

So, with that being said, would you run the engine at 0.037" clearance? 0.035?

I started doing a stackup using metal expansion coefficents at the max surface temperature it could see(600 deg F), large pin and main clearances, and wasn't even getting close to that distance...haven't calculated possible rod stretch, etc.

I did however, see an article by Steve Dulicich where they used the 0.055" head gaskets with the same pistons sticking out of the deck +0.018" and closed chamber heads, and it worked...but then again I don't want have this thing get ruined.

Given your not going to turn the engine much past 6000rpm, I would be OK with .035. Measure all of them to be sure. I've run .030 to 7000rpm but it was with H beams, forged crank/pistons.
Brian