You'll need to verify the initial timing, the amount of mechanical advance and what RPM it comes in at along with how much vacuum advance is available, this could easily be 20º. In other words, you could have the initial timing set at 10, fine, but the dist could give 30 mechanical and 20 vacuum, giving you a total of 60 and a nasty pinging problem.
This engine is really marginal for todays gas, it was made to run 100 or so. I recommend you have your dist gone through at a shop where they have a dist machine and know how to use it. A short, late curve with limited vacuum advance might make all the difference here.