Sounds like good advice.
The engine started life as a 68 2bbl. However, it was rebuilt along the way, and before I got it.
What I was looking forwith respect to timing was which cam is in it? I guess from what you know, we don't know. That's OK. The curves aren't that far apart.
a few years ago, initial was 18 degrees and adding 20 degrees of mechanical advance all in by around 2500. Seems like a lot of initial timing, but with this and the vacuum can attached it pulls 18-20 inches of vacuum, and has a clean idle. I keep reading that the engines like more initial with the newer/ethanol fuel.
It is alot. That amount of initial is needed on relatively radical cams, maybe around 240* at 0.050 in 383.
18-20 " of vacuum is a good indicator that the cam is quite strong at idle and should be fine with stock initial timing (pre-CAP). It probably could be made to work with the emmissions specs but that's just a headache for what your doing and hurts economy.
You can't really use vacuum to guide setting initial timing with a manual transmission. Out of gear, all engines love lots of timing and lean mixtures. Life's easy. Too easy. Start to put any load on and there's no power.
My suggestion is to go for timing curve based off the 1968 curves for a 2 bbl automatic and a 4 bbl 4 speed, but use the '67 initial.
Initial timing for all 383s in 1968 was reduced to reduce certain emmissions. Just use 12 - 15* BTC and try to get the idle speed down. Factory was 650 rpm with emmissions. You should be able to get in that ballpark.
Try the black or orange spring on the one side, and the secondary spring should have an long loop so it doesn't engage until the rpms are up around 1500 -2000.
If you don't do that, my experience (small block) is that on longer trips the engine will ping at part throttle load.
With the YH advance it is very difficult to slow down upper end of the advance the way the factory distributors did. Just do the best you can. If you can keep it from hitting 38* until after 3000 rpm you'll have done well. You can then use vacuum advance, and tweak it to provide around 56* when crusiing on the highway and it shouldn't ping at part throttle. 56 is what Direct Connection recommended as a target for b/RB engines and guess what? Shop manual shows a 383 4 bbl vac advance can add 24* at 15"Hg. Add that to factory curve which shows 32* at 3000 rpm and its 56*. There seems to be a pattern here.
