[DanEC]

What you can do to see if it’s a flange issue is clean the surfaces and with a big felt tip marker color them black, or apply a light coat of black paint. For a sanding block on an aluminum intake port surface I used a new, 24” aluminum level which was about 1-1/4” wide and dead straight as far as I could tell establish with my steel straightedges. I put a strip of 320 +/- self adhesive sandpaper on it and block sanded across the ports a few strokes to see what I was dealing with. That will pretty quickly tell you if you have a minor surface irregularity on the ports or a major one that may require surfacing. If it doesn’t look too bad you can probably switch to some 220 and with some work get them pretty flat - although blocking steel will obviously be a lot harder than an aluminum manifold surface. You might even carefully be able to address high spots with a side angle grinder, going slowly. It straightened out my intake mating surfaces up and allowed them to sit and seal up tight. Just a thought.