Yep, 6.4's are compound turbos. Head studs may be in the future but I'll back it down on power a bit and watch egt's when towing heavy. I have the tuner set up to only add power when up to operating temp. That is one of the biggest killers of head gaskets cold cylinder temps and lots of advanced injected fuel. Gotta make sure everything is up to temp and tight before thrashing on it. Twins are the way to go IMHO the only caveat when doing aftermarket twins is sizing. The 6.4s have one vgt turbo which helps allot with running wildly different hp levels. When most aftermarket sets are sized for somewhat narrow power levels. If that makes sense? Not to say a good set of twins won't handle big power they just won't tow as nice as a specific towing set. You probably know all this already though.