1973 B3 Duster

I just started messing with the tuning and everything I read and recommendations here said it needs 18-20 degrees initial, so that's where I have it right now. I bought one of those distributor advance lock plates from FBO and used the 14 crank degrees mark, and my total wound up in the mid 30s and then I have the vacuum on top of that. I'm listening for knock and don't hear anything obvious, but I am a little worried I'm missing something subtle.

My carburetor got replaced by the shop with an Edelbrock Performer 1400 (the street legal version). The way it was originally tuned, there was manifold vacuum on the ported side (the manifold side isn't working correctly and I'm not sure why, but I'm not using it). After advancing the initial to 18 or so, I was able to back the idle screw out enough to get nearly 0 vacuum on the ported side at 750 RPM. The 750 is a little rough, so I may go back up to 800 RPM at some point, but that will put vacuum back at idle.

I asked my shop about changing the distributor advance, and he said you just change the springs (nothing about limiting total). He told me about drilling holes in the butterflies, but that seemed strange to me at the time. I didn't see any reason to drill holes in a "good" carburetor. Maybe I'll need to revisit that at some point in the future. The carb has vacuum secondaries and I'm not sure how adjustable the 1400 is since it is street legal. It doesn't have all of the slots on the top of the carb that Edelbrock shows for replacing the metering rods.

I didn't realize you could run a motor like this on 87 octane.
Thanks!