IMO just find a GOOD MACHINE SHOP. Round is round, square is square, flat is flat.
When I first got into this, I asked my machinist if he knew Mopars. He said "It's a chunk of iron, it doesn't know what it is". I've never questioned him again, and never had a problem with his work.
That is true to some extent but it is nice to work with a shop that knows enough about Mopars to know where to buy stuff. A really good machinist who only works on Chevy engines probably won't know where to buy special Mopar parts and tools. He might not even know they exist. And he probably won't know little tricks like using AMC lifters for pushrod oiling or where to find billet rear main seals and stuff like that. Even Mopar guys don't know a lot of these tricks which is why there are about 100 questions a day posted to this board.
