Hehe, well if you have never heard a 420A with JE's in them before, then anyone may freak out a bit :) I was lucky, because I had already heard what it sounded like before I built my motor.

If your slap doesn't go away when its fully warm, then your machine shop may have used a bit more piston to wall clearance than suggested. This isn't an entirly a bad thing, because now your motor is capable of handling a ton of boost, since more boost means more heat, which expand your pistons even more. I've known some 4g63 guys who purposely give a ton of wall clearance just for this. I don't know for sure, but excessive wall clearance *may* have a slight effect on how quicly the cylinder walls wear, but i'm not sure on that.

And for the breakin, you dont have to be super anal about it, just drive the thing normal. Dont baby it, but dont exactly redline the thing right away either. I lightly boosted several PSI right after I got my motor running and driving. Did a compression test at 150 miles, and got 195 psi accross the board. I've been beating on my motor since about 300 mile mark, and still runs like the day it first started up, and still has great compression(approx 30,000+ miles on it now)