5.7 vs 6.4 SRT build and swap

For my 70 Duster, and this is what I want. A 600 horsepower, Holley EFI tuned on methanol drag race engine that can also run on pump gas if I want. The decision needs to be made on how to get there.

If I were to buy a running SRT 6.4, swap the cam, add some headers and tune it on alcohol I think it would be close to the 600 number I want. The factory compression is pretty high, and they are build pretty stout. The 5.7 would require an entire engine rebuild with rotating assembly, head work, etc... Cost wise the 6.4 would be less expensive to get the same power numbers I believe? That of course depends on scoring a good deal on the engine to begin with. Both engines would require the same manifold, headers and basic swap items.

What are some thoughts? 600 is the number I picked in order to get the car to run 10.20s at sea level. It weighs 3300 with me in it, 727 and 4.10 gears. Right now it runs 10.70s with the LA stroker that has disappointed me.