Or more importantly, what is the difference between the valvetrain parts in a 2004 truck 5.7 and a 392 crate motor/dragpack engine? I bought the Dragpack cam and can buy the springs that came with it also. Are the stock 5.7 locks and retainers good enough to use? Due to having stock cast pistons and rods, the rpm will be kept down some on this deal.
The Dragpack motor came with spacers under the springs that appear to be made to take up installed height to get close to coil bind. They are different thicknesses for intake and exhaust. Also what is the rocker ratios for both engines, and will the heads need any mods to handle the lift of the bigger cam? Does any one know how much lift and duration you can roughly get away with before you run out of piston to valve clearance for the 5.7?
It also occurred to me that if I have to spend a fair amount of money on little items, I may as well look at a newer set of Apache heads for what, about $600?

I am in the planning stages of my own Gen III Hemi build, from what I have seen the stock rocker ratio is 1.65 for the 5.7 unsure of the dragpac. Apache heads won't work on 5.7 block, but the eagle heads (09-current) do fit. Eagles will out flow the 6.1 on the intake side but are lacking a little on the exhaust compared to the 6.1 head.

5.7's have a pretty low lift cam (.472/.460"). 6.1 and 6.4's have a much higher lift setup (.571/.551, .577/.537 respectively). 1st level upgrade then would be to install 6.1, 6.4 springs. They are also installed at a different height than 5.7's, so removing the shims might be a given for the application. Even though flow numbers are better on the 6.1 than the 5.7, there is controversy over which head produces more power due to air velocity. A real good compromise is the VVT (Eagle) head. Has 6.1 port flow, but slightly smaller valves to keep air velocity up. Theory has it that the 6.1 and Eagle heads flow the same, but the Eagle head will produce more power. Plus the Eagle head has a much smaller chamber than the 5.7 or 6.1, raing compression on a stock 5.7 substantially. The bigger 6.1 cams have a smaller base circle cam, and use longer intake and exhaust pushrods than a 5.7. Rocker arms are the same. Any head will physically fit onto any block. 6.4 ()Apache) heads might have valve fitment issues on a 5.7 block, though. Very big valves. Also, the Apache head is not recommended for boosted applications. Too thin, will lift.