New to the mopar world,Need help with 318 build..pleeasse..

I don't think a dial caliper that accurate enough try it.
No magnums don't come with roller rockers but ya you can use chevy along as the got the same stud size. The push rods would have to be longer and be able to past oil and you might need new lifters if your can't past oil. But roller thumper cams like $300 and you can reuse factory lifters by time you buy push rods and flat tappet lifters you might be half way there to a new cam. Any year Magnum should be fine 5.2(318) if you want a revver 5.9(360) torquer same heads.