Since you have mopar performance distrib there's really no reason to run the vacuum at all. You'll just set your initial timing at 20 BTDC for now and then see how much total timing you have at 3500 rpm or so. Do you have an adjustable timing light so that you can dial in? That is a necessity to check your total timing.

Even at 10 BTDC you should have not felt a power loss. I would also look at fuel pressure and make sure you don't have a kinked line or something. Make sure your float levels are correct and your linkage is not binding on the secondary carbs. Sounds like it may be running majorly lean too so definitely double check the carb float levels.

After that I would also run a compression test just to be sure that you didn't wipe a lobe. If it idles smooth though you're probably okay. You would tend to hear it if the cam got smoked. Remember the '78-'79 chevy camaro with the lobes that wiped? Nearly everyone I knew with one had the cam go south. Even the trucks tanked. I can still remember hearing them and the sound the engine made with wiped lobes.