Drilling the throttle plates

Need experiances with drilling the throttle plates.

OK , it's a "DORF:" It's a 77 3/4 ton F250. Worked over 351 with a Edelbrock Performer.

Problem: If the timing is set where it should be, the throttle plates are open so far the ported vacuum to the dist. is active causing the vacuum advance to be in at idle, I have to advance the timing so far to get it to idle and not have the ported vacuum active that it's not good for the engine. It runs very good advanced and equally good retarded, however it idles irratically when the dist. vacuum advance is active at idle.

Would it help to drill a hole in each primary plate so that I might be able to close the throttle plated more and get the ported vacuum port so it's not active there for being able to set the timing back down?
If so, where do you drill the hole. Towards the front of the plate, or the rear of the plate or does it matter? How big?

Any help and advice would be appreciated.