Used PAC's
 

I have a buddy who is willing to just give me a set of PAC 1519's with like 12k miles on them, they came out of a cammed C6 Vette. I plan on camming my car over the summer and I was wondering if I should even bother using them. I was planning on doing a custom grind at around .239/.595 at 110 lsa on an M6. Should I consider this, or just buy brand new?

Have them rate-checked by a machine shop.

Buy new. I would never run used springs. Look into some PSI springs or Pac 1518's.

Your cam profile might want a DUAL spring matched with it's lobes for better control. Consult with your cam company.

The aftermarket springs like comp and pacs are only good to like 15k milez max...since aftermarket springz have higher lift capacity they are more brittle which means that they have nowhere near the fatigue life of stock springs, most swap aftermarket springs after 10k miles...in my opinion u are just begging for a dropped valve with those springs!

Its always best to buy NEW!! Trust me, Ive had 2 spring failures, and neither were pretty.

Even this isnt ideal. When my wife's car dropped a valve, I checked the remaining spring pressures, and they were all within a couple pounds of what they should have been.