Header Repairs

This is not an for an A body ,but I value the expertise on this forum.I just got a set of used tri-y headers for my 440 Ramcharger and it is evident that they have been leaking around the corners of some of the ports.The sealing rings don't quite match up to the exhaust ports.Would it be better to build up the corners with weld and then grind flat to match the existing rings or just plane the whole flange flat? It has been suggested elsewhere to split up the flanges after so the individual tubes can move...thoughts on this?It makes sense to me but manufacturers don't do it.

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