I looked into getting the machining done down in Tijuana, and the guys said you’re really only saving a couple hundred bucks to get it done right, so it’s not really worth the hassle.
Machine work or not, roller or not, if you do a solid lifter cam in the appropriate range (as in not conservative but not like .700 lift) you'll get to your goal with heads that can flow well. Plenty of people have made 400 horse 350s with 882s and conservative cams with basic effort. Hell, you might even do it with a hydraulic lifter. Doesn't seem like a good idea with a hydraulic lifter though.