Without knowing anything about the engine other than it has two carburetors, you can do a baseline of 12 degrees BTDC initial, 10 degrees vacuum advance, 38 degrees BTDC total. In reality, your initial might work best anywhere from 6 to 20 degrees, with 4 to 16 degrees vacuum, and up to 42 degrees total. Total advance is your initial plus your centrifugal advance, minus vacuum advance. It may run better with manifold vacuum or ported vacuum. A lot of factors go into ignition timing like compression, cam, engine condition, coolant temp, carburetor tuning, fuel specifications, transmission, final drive, vehicle weight, altitude, and probably a dozen other side elements. You really have to tune to what the engine likes. Another element that is easy to tune on an MSD is the ignition advance curve. That one is a lot more difficult because you have to understand how the springs work and how they shape the advance curve and how that affects engine performance. I like a curve few here would agree with, but that's how my tune up works for me. Go slow, read and understand, experiment. Always have a documented baseline as a place to get back to when things turn to crap. Always document your changes and make only one change at a time. Evaluate the affects of that single change. When tuning, always get the ignition dialed in before you start fiddling with the carburetor. A strong ignition will crutch a weak carburetor. A strong carburetor will not crutch a weak ignition.
