If the heads are off, would it be best to put the weld on the inside of the head, which would decrease the air volume slightly? Or might the heat soften the infused hardening of the head (e.g. w/ a ...302 head)?
IMO, while probably the best way since it’s a super permanent deal, it’s overkill - which isn’t a bad thing. I’ve seen people use JB Weld and even aluminum foil crammed in there really good.
The welding should be ground down if it’s any high. But no, the volume decrease isn’t anything that would show anywhere and NO, port velocity wouldn’t pick up. If it did, that would be about a 1/4 inch of welded.