Sounds like it's going too lean. When it stalls, is it popping or surging, or is it just not revving up ("Falling flat on it's face") and then recovering? Surging/popping is too lean, "falling on it's face" is generally too rich.
* Plug the SCV port in the carburetor and forget it's there - the carb doesn't know or care. (now, if you had a LoM distributor, they care a lot - but you don't)
* Manifold vacuum is best. Ported vacuum was only introduced as a way to increase combustion temps at idle for emissions - nothing else, no matter who says what (my source is one of the GM engineers who worked on ignition systems in the 60's-70's.)
* You should see a nice steady squirt of fuel out of the accelerator pump nozzle just as soon as the throttle moves - like a water squirtgun.
* Given the above checking out, disconnect the accelerator pump and see if/what difference it makes - it'll give you a clue what the engine is wanting. If it then revs good, then the accel pump is flooding too much fuel. If little or no change, then the accel pump is likely not shooting enough fuel.