Vacuum reading help.

I agree that setting the valves is the first logical step, followed immediately by a compression test. If you have a burned valve a compression test will show this real quick. That being the case, the cylinder head needs to come off and go to the machine shop to be rebuilt ($500 to do it right). An engine must be mechanically sound, meaning 12 sealing valves and even compression before you can ever hope to get it to run right.

A clogged or sticky PCV valve can cause rough idle. The early metal style can be cleaned by soaking them in lacquer thinner overnight, or blasting them out with carb cleaner spray. The later plastic ones are easily replaced

A worn out distributor can cause no end to poor running issues, remember that 90% of carburetor problems are ignition related. Electronic ignition is a great upgrade over points, highly recommended. If by HEI you mean adapting some sort of GM based distributor, well, it's your car...