Another timing curve question

Plot the slope and see where it might be if it continues as a fairly straight line.
Its tough without knowing either the true initial or the actual maximum advance. I'm not fond of spinning the engine in neutral to 5000 rpm holding the light there, nevermind 6 or 7!
Maybe the best thing to do is get it on a distributor machine before hitting the track. It will have to be one that goes up to 4000 rpm (distributor rpm).