Just a general rule of thumb with these things. Anytime you find yourself having to run more than about 10-14 degrees initial timing to get the engine to want to idle well and make good vacuum at idle speed the cam far from the ideal choice for the CID and static compression ratio. Not liking any less than 36 degrees locked-out timing tells me cylinder pressure is pretty low at idle speed due to the overlap bleeding it off and that the build isn't overly happy with the intake closing point.
Not a "big black" cloud over the build but observations made from neary 50 years of building engines, dynoing them, putting the in cars and getting track numbers on them, plus "custom tuning" thousands of them for a living. In any and all cases with engines like that they are going to have considerable "reversion" at lower RPM's which requires MORE timing and fuel to keep them happy......FWIW......
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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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