Low Vacuum Issue/Big cam

I'm an old school MOPAR guy - Pre-1970 with no experience with the Vacuum accessories.

1974 Dart Swinger, power assist disc brakes, 318 2-bbl motor, electronic ignition w/vac advance, 904 stock converter origninally.

Last weekend, I installed new Mopar 2x roller timing set, 284/484 purple shaft hyd. cam, (Degreed straight up) 360 J heads pocket ported, cut .060" comp face and .020 intake face (2.02/1.60), torquer 360 manifold and Edelbrock 625 carb. Timing set at 10* advanced with vac. adv. plugged, goes to 20* adv. when hooked up. I cannot get it to idle consistently below 1500 rpm. It will idle fine for about 30 seconds then starts to drag down and eventually dies. I replaced all vacuum lines, verified that there are no engine vacuum leaks. The vacuum amplifier is still in the system and holds vacuum. Is there a vacuum switch that I'm missing or is there a trick to getting enough vacuum to run?

I have not checked the actual vacuum reading as the car is at the muffler shop getting piped from headers to mufflers.

Thanks!

I've run this set up in several pre-70 BB and SB cars without problem.