You probably won't be able to beat $649 you paid for those Vortecs. If you get used heads you shouldn't just bolt them on. They are going to at least need to be cleaned up and checked and probably need a valve job, seats, springs, valve locks, retainers maybe valves, milling and you should really get them hot tanked and magnafluxed before you use them to do it correctly. Used heads aren't necessarily the better deal just cause you can get them for $100.00. Nothing would be worse then bolting on a set that isn't re-worked and having them piss coolant everywhere because they aren't flat or worse cracked. I would return your heads and get these
http://paceperformance.com/index.asp...D&ProdID=67722
....to save yourself some extra money. They outflow the bowtie heads out of the box. You can beat them for the price, just check what springs come on them, I think they are good for .550" lift