they should be easy to find- pretty much any GM car made after 82 or so had them. there are 4 versions, tho- a big cap one that has the same cap as a regular HEI, and a small cap setup with an external coil. neither of these will have a vacuum advance can on it. some mid 80's trucks had a computer controlled HEI that has a vacuum advance can on it, as well. the 90-93 Caprices with the TBI 350 or 305 have their own distributor, which is a small body external coil setup, but only fits the bigger hole in the B body TBI intake that allows you to actually take the thing out with the engine in the car.
you don't plan sincerity.
you have to make it up on the spot.
wanna hear about 20 years ago when i was too smart to know any better?