The best advice would be to use what works best for your combination. There are some combinations in which you will have no choice, mine is one of them. The 455 currently powering the Ventura idles at 6-7" of vacuum at 750rpm using a ported source with 10 degrees initial timing. The plates are opened sufficiently and the idle is very stable with no noticable change in and out of gear. If switched to a manifold source vacuum increases to about 10-11" and idle speed goes to about 1000-1100rpm. When the throttle plates are backed down to provide 750rpm idle all is still fine. As soon as the engine is placed under load or in gear the vacuum falls back enough so that the vacuum advance is disabled and the engine immediatly stalls. The only cure is to raise the initial timing to about 14-16 degrees, then the engine expiriences difficult hot restarts.
With engines with mild cams and plenty of vacuum at idle it really matters not what source is used unless you add in a bunch (20-30 degrees) of initial timing with the vacuum advance. Then problems occur from too much initial advance, probably some of the symptoms described in the original post......Cliff
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https://cliffshighperformance.com/
73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile),
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