Are you aware that a stock 4age/4agze headgasket can hold 20psi and more? 20V gasket is different to the 16V gasket. I'd personally not bother taking the head off if you're only going to run low boost, just tune for the boost you plan to run with a full aftermarket ECU, not piggyback. EMS, Microtech, haltech, autronic, wolf, link are all capable of running it. There's a stock AE101 20V turbo with TD04L, FMIC and microtech over at twincam.org forums, TRD16 owns and built it. still at 10.5:1 compression too. http://www.twincam.org/forums/index.php?showtopic=12579