Getting a smallblock to rev

Seems to me you are thinking wrongly. What is RPM going to gain you, besides, broken parts?

If you are stuck with stock heads, breathing might be a problem. I say build the best engine you can with what you "got" and then change what you need with gearing and tires.

I'll trade high RPM, short life for torque anyday.

I'm thinking a regrind of a 68 340 stick cam? Better heads if legal? Certainly mill heads/ deck and change pistons as necessary for more compression. Run a mechanical cam if you can, stock 273 rocker gear.