My 340 build

No, you're not over thinking it. That is getting down to the minimum piston-to-head clearance I personally would run. The local circle trackers have run down to .025" at the least but not regularly it got on the margin of impacts when things got worn. I have put in a slightly thicker head gasket before with .005" out of the hole..... but that was for someone who I knew would never take care of the engine and would not take notice of any rapping sound from the engine ! So he got some extra margin LOL.