I did some testing on my engine (compression and leak down). I had one bad value. I freshen up the engine (gaskets, seals, new oil pump, new water pump, timing chain, basically everything easy to replace when engine out. I rebuild the heads.

You have found some puzzling issue swith your heads. I have built a few motors and I would suggest you take your engine into a engine builder and get some advice. You need the heads done but not sure about the welding. You can always find other heads so why risk fixing bad ones.

I have 2 engines that we did. One I freshen up and the other a rebuilt. I made my own engine stand. Have a look at my YouTube "reels".

Stick with stock...