Timing curves will depend on the package, but for most of the ones I've built, you're about right if not a little too much, too late. These engines don't need a lot of timing to make up for anything so you can run 18-20 initial, and if it's a smaller chamber and quench dish run with tight quench, the total will be closer to 30-32. That leaves some room for the vacuum advance amount, which I will always advise be run on a street car. You should also be able to bring it in a little faster because depending on what your gearing is (most big strokers have mild gearing) you want to have the advance "in" right around your typical cruise-at-50mph rpm. If it's built properly it should be fine with that. If it's a wider quench, or cam too small, you may not be able to do that with 91 from a local pump.