I don't see how you can do a double spring with the stock rockers so it looks like double springs and rockers. Piston to valve is really tight on the intake side and I just don't have the room for a Ti valve with the additional margin. I have the valve pockets as deep as they can go. When you start getting away from stock these engines are pretty tricky. I may just sacrifice the power and put a milder cam in it. I just don't have the time to keep going down this road.
I would assume Craig @Thitek simply specs a beed lock groove lower on the stem to run a double spring retainer that works with stock rockers.
Even the 2.16 valve that Thitek uses is extremely heavy compared to stock Apache valve
