I like the Lunati 268 cam specs, it is a little higher in duration and a little lower in lift than the hughes cam. Probably more advantageous with the x heads. I think the compression ratio of a stock 340 (10.5?/year?) might eliminate the whiplash cam as an option, which hughes specs for lower compression engines in the 8 to 1 range.
Either of the other 2 cams would probably be better with power brakes.
I agree, more about the motor has to be determined before doing anything, especiallyreplacing the cam, especially with gambling with new cams and lifters.
EarliA had a good thread recently determining cam specs with the cam still in the engine, and the engine still in the car.