go for gt17 saab turbo and fusion fabrication manifold that's what i have and no need to cut bulkhead. only part hard to find seem to be turbo carbs with locking ring around dashpot. if you get a full tubo engine then can keep your n/a one as spare and probably save money in long run.
Are Fusion still on facebook? The diy flanges & bits seem to have disappeared from fleabay.
https://www.fusionfabs.co.uk/
An old thread I know, but there are Cad models/patterns for flanges on GrabCad to download. Search a series and there are a few interesting things. Just send to your local laser cutters for pricing or there are some on ebay. The patterns I put on Grabcad fitted without issue to my 998 and I think they are OK on 1275, I just haven't made a manifold yet. I made them for 1.25 or 1.5 diameter tube , I can't remember, but there are notes on GrabCad.
Jeff