when my old 165 hp Mercruiser distrib was worn out, I found a guy in south Delta who would send them out to get a new bushing pressed in. He was an MSD igntion retailer. He had previously worked with timing Funny cars at Mission raceway. He lives down on 25th avenue. He told me to use the initial advance of 14 degrees. Told me that unleaded takes longer to burn. The guys at the machine shop can tell you your head will last about 1000 hours. Then you need to rebuild them.
Are there some different distribs you can buy that have different advance curves?
Is the distrib that you have recommended for this engine?
I got a new distrib for a regular car, removed the vacuum advance, plugged that hole, and used it with just the mechanical advance. I was tired of spending money on rebuilt distribs, so far from my house at that time.
Hope that there is some part or way to tighten timing chain over the years to keep the timing as good as possible.
You may need to see some racers with dynamometers, or hang out in the pits at Mission dragstrip.