Quite a common problem and you are correct that welding should be avoided as far as possible.
Somebody has over tightened the TPC (Transfer Port Cover) bolts, no doubt they had gasket failure and air leaks.
As faces on TPC’s are on same plane then the matching faces on the case and barrel need to be in the same plane so that the TPC will sit evenly on the gaskets.
Because of manufacturing tolerances and deviations, they rarely are.
For interest, If I am making a new engine and barrel, I assemble head to case and machine together.
I never use TPC gaskets and use RTV silicone instead.
Clean and degrease both parts
Put some silicone on a card
Apply a thin layer of silicone on the faces of the TPC
Tap down silicone evenly with your finger end if not even
You must not use too much as it will squeeze out inside and slightly restrict flow area.
Now assemble and just nip up the bolt moderately so that you do not stress the cracked casting too much
You will see a little silicone squeezed out all round
Wait 24 hours and with a scriber or rule remove excess silicone
The basis is that the silicone will set in whatever gap is left between case face, block face and TCP faces
If due to manufacturing inaccuracies there are slight gaps in some places, the silicone will fill them
The silicone will also have a degree of adhesion, so you do not need to tighten the center bolt too much
Kind Regards
Roger
