Here's another question to throw out (Since 'm in the same boat, about to order and wondering if this option is worth it):

Are hardened valves and seats an advantage towards reliability/long life in a gas engine assuming that I may never modify the truck to CNG/LPG? The option is only about $315 and the valve job I had done on my '94 460 (at 200K miles) was a heck of a lot more than that.

Other question is the intake manifold, I'm wondering how the engine is affected by it, is a flow difference (losing/gaining efficiency) or is it just to allow some sort of alternate gas fittings?

Is the Ford Engineer still on this board?

Joe