Wasn't trying to be anecdotal. Just pointing out that initial timing is pretty important and those two stories popped right up in my little brain. It can make or break the set up of a Weber 32/36.
Back to the OP, it will depend on your altitude, your desired in-gear idle rpm, engine condition and probably a host of other things. I usually recommend starting at 8* and just drive test the thing over the course of a week or so while going up in 2* increments. It'll probably behave better to a point, then it won't really seem to make a difference and, once you get to that point, a further increase in base timing will start to sound like an engine full of steel marbles. Make sure you don't go there!
Like I mentioned, on an old stocker, especially one with ping-prone "smogger" heads from the '80s, you won't want more than 12*.
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DO NOT set initial timing to the highest vacuum reading. It's likely to result in far too much advance. Use the vacuum gauge for the mixture screws on the carb. Use a timing light for timing.
Here's what I recommend. The total timing (initial and centrifugal) at the upper RPM ranges is what I've found to be the most critical for performance. IMO, you should strive for 30-35 degrees total at around 3000 RPM. Once you achieve that, then let the initial land where it lands. My 258 ended up around 11 BTDC initial.
Then hook your vac advance up to manifold vac, set your idle around 700 RPM and dial in the mixture, and enjoy.
If you're ever willing, I'd love your help with this. Nothing better than a lesson from a knowledgeable jeeper. Just let me know, and I'll head out your way. With beer!