Any downside to purchasing a set of used head studs? Anything to look for /watch out for? Also, are the 6pt or 12pt better?

 

I wouldn't see a problem with it as long as they haven't been torqued a 100 times or run on a very high boost motor. As for the 6 or 12 thing, it's the same stud with 6 or 12 point nuts. The 12 points disburse the torque more evenly around the circumfrence of the nut, but either will do you just fine. Most use the 6 point because they are less prone to stripping.