Rallye Wheels - Help Needed

The center cap is a '72 only SBP rallye wheel cap so I bet the wheels are '72 vintage too. (not that it matters in your case)
Drilling the top off the lug nuts is a good idea, and then use penetrating fluid on the exposed end is a good plan of action.
That might also relieve some tension between the stud and the nut itself with the vibration and all.
Also, what I would do is apply some heat with a butane torch to the side of the lug nut making sure that you are pointing the flame away from the center cap itself.
You don't need to heat it up red hot, but get it nice and warm and try to spin it off with the aforementioned breaker bar and a socket that fits well.
I'll bet that they move if you do that.
If they twist off, then you did all you could have done given the circumstances.
You were going to replace the studs anyway after all of this, right?
The only thing else you could do which is a pain in the *** and difficult to do is to use a die grinder and grind away the side of the lug nut on one of the flats and it will for sure come off.
Finally, first try left hand threads to turn it off (clockwise) to spin it off and if that doesn't work, try spinning it counter clockwise if that doesn't work because you never know what someone has done in the past...
Good luck, and let us know how it works out!
One thing for sure, I would change all of the studs to right hand thread after all of this and use anti seize on the threads...