Surely it can be done, but there are limitations of how much iron can be removed from the stock head castings to provide upper end flow. Then again, with gearing to keep it away from 5,500+ RPM that wouldn't be a real problem.
As for the '57, it isn't mine, it was just my project. If was rewired complete to accomodate the ECM, fuel pump, all the sensors, etc. The only thing it doesn't have is cat converters and an EVAP canister, but I programmed those out along with the inputs for the auto trans. It has a TH350 but no VSS, no top gear switch, and no TCC. With the programming changes, the ECM doesn't care.
Some of the MAF/FP wiring:
The power wiring, ALDL, and MIL:
And a closer look at the engine:
Sorry for hijacking the thread, but he asked...
As for the Caddy heads, you may be better off if you start with 651 castings or get out your wallet and shop here:
http://www.cad500parts.com/