Connected, it's 30*, at idle, out of gear.
It must be a manifold source at the carb, since it's advancing 18* at idle with vacuum advance connected.
That said, I ran the tests you asked me to, to figure out total timing.
Vacuum advance disconnected, I revved it to 3500, at which point it stopped advancing, staying at 30*.
Thats 18 being added by the mechanical advance, you want to be at about 34-36 here
Vacuum advance connected now, I revved it to 3500 again, and it stopped advancing at 50*.
Thats another 20 being added by the vacuum advance. You need to look at other areas now, can you park this car for a bit, if so pull the dist and make sure that it is clean and not worn out and see if it has been modified, 18 degrees on the mechanical side is not in keeping with a stock HEI but lets give that a rest for now.
I mentioned that before you get into the tuning you need to ensure that all aspects of the assembly are tip/top that would include the valve train. Have you done a compression/leak down test lately? how many k on this motor? did you degree the cam when you put it in? did you ensure the balancer pointer is in fact at TDC? timing chain type is of little concern here as long as it is in good shape and installed right, vacuum reading interpt,,, look at this http://www.classictruckshop.com/club...ts/vac/uum.htm
you can use the vacuum gage to help narrow down issues, there are other sites with annimation, hope this helps,,,keep on it,,,the carb is going to be next.