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.
My thought wasn't on whether the shops that don't do much Mopar work can do it correctly, as much as are they familiar with some of the common mods (e.g., enlarging the BB oil system passages) that the more experienced shops do as a matter of course.
EDIT: Funny thing I found is that the shops that aren't "Mopar Only" are also more open to options on how/what can be built. Example: Every "Mopar" machine shop I've spoken or dealt with has been very firm on whether they'll upgrade with aluminum main caps vs steel main caps, and/or use girdles. Pretty much NO middle ground, despite any experiences or observations you can provide them that goes against their philosophy.
The non-Mopar shop that's done my last couple of rounds of block work is perfectly willing to listen to the pros & cons about both approaches. In the end, he thought my idea of using aluminum main caps for the "shock absorption" benefit along w/ a girdle to stabilize the caps was a pretty good idea, given what he knew -- or we talked about -- are the deficiencies of OEM RB blocks. I think his comment was: "I don't see any downside to doing both".
