won't hurt anything to try both,
you will see a change, ported vacuum is "0" until ? 1500 rpm+, you have no vacuum advance at idle
so when drive away normal at a green light, it takes a little more peddle or excellerator pump (richer) to compensate for no advance
Why is it there? I don't know this to be THE reason but there are "dual" vacuum advances on some Ford dist, it's a push/pull deal, never used one but makes sense.
My car sucks on ported, runs great on manifold, 90% sure yours will also.
Gona buy that Demon carb, ask them also, direct connection, vacuum advance and carb rich/lean