YEAH!! My 390 ha no provision for ported vacuum. I plan to put a check valve in line this spring to help maintain full vacuum to the advance. My advance is set up to add timing as soon as the engine starts and idles. I can kill vacuum and raise the timing and three's no bog, but it makes it hard to start when the engine temp is on the hot side.
The engine in question is an old 153 cid. 4 cylinder out of a '67 Nova.
This is what I worked out for switching my Monojet on my Chevy 250cid with the Holley 390cfm:
