Rough idle, need help

[Slowleak]

That sounds normal. You should have zero vacuum on the passenger side port at idle. That's your ported vacuum. If you crack the throttle open you will see vacuum.

Is your vacuum advance running off the manifold vacuum on the drivers side? If it was mine, I would have the distributor vacuum hooked up to the ported vacuum. You mentioned that it would die when you shifted to reverse. Using ported vacuum will make a big difference with that. You will have to advance your base timing if you switch to ported but it should idle much better and fix the problem with shifting to reverse.

If you are dependent on manifold vacuum at idle to keep the timing advanced then when you shift gears the engine speed drops because of the load, vacuum drops, advance drops, and that causes the idle to drop even more which drops timing more and idle speed more, and it dies...

 

[September 1972]

90% of the time it's ignition related.

Junk the petronics would be the first thing that I would have done. After I raised your hood you went to get us a couple of beers. By the time you handed me the beer the petronics would be in the trash.

The other possibility is the carb is restricted or otherwise defective. A spray bottle with fuel or a propane torch will confirm or eliminate that possibility.