Apache heads won't work without some block mods. Eagle's will bolt right on but to get compression down you need different head gaskets that are ~$250 ish and probably new pushrods. The Eagle's won't do much for you without a cam. I think your original plan is sound. Good luck.
Why would he have to mod the block for 6.4 heads? I haven't had to for any of the swaps I done...
Oh and my 2007 5.7 I bought from the auction with 2 dropped valve seats and rusty crusty antifreeze blown all over the engine compartment, I have seen tons of dropped seats in 5.7s and EVERY. SINGLE. ONE. had signs of over heating. I proceded to put on a pair of eagle heads I had laying around with stock head gaskets again no issues except it now needs 91 octane to keep the knock sensors from showing activity, has significantly more power and it gets much better MPG than my 06 with a bone stock 5.7 with less miles (also an auction pickup with dropped seat and lots of signs of overheating).
