Ron Sutton has a good explanation on basically everything you need, I am thinking of getting one of those distributors or an adjustable ignition box.
Keep in mind that I am no expert.
But another way to help the Idle is to plug vacum advance straight in the manifold, so it pulls advance at idle. It really helps alot. And I like vacuum advance for those situations when the engine likes lots of timing. In leanburn situations and less throttle openings/cruise speed. Since it "adjusts itself" Just watch out for detonation.
And to help some more on the idle transfer slot, could be to run an PCV system, so the engines get some of its air through that, so you can close the butterflies some more. Even though it is not "racey" to have PCV.. HeHe
It works for me atleast, I have not needed to drill throttle plates either, but I also only have 236-242@ .050 Hyd. Roller. 461cid. So its a bit more "street friendly" maybe.
On the other hand, I would guess the baseplate on the HP carb does not have so many vacuum outlets maybe?