You can fix the lumpy idle and low vac running manifold vac, I know you know this and have tried it, but keep messing with it. you have to limit the amount the vac can pulls usually around 10 to 15* or you will run into bucking and jerking at very low speed and or cruise. Set your timing as usual (no vac), then plug the line for the vac can into full manifold vac, your idle will instantly go up, as will your timing,(timing will increase by the amount the can will supply) turn the idle screw down to desired idle rpm, leave the ported vac port pluged. once you are pluged into manifold vac you only have to dial in the vac can (limit it to 10-15*) and you should be good or real close. Don't mess with the timing anymore after you set it and plug into manifold, all of your adjustments will be with the vac can, and you have a adjustable can. You will see cooler temps, better gas mileage, better throttle response with manifold vac. I know you know this already, but if you really want to switch we can work through it together, it really boils down to trial and error with the vac can. (getting the correct amount)