make sure that you time the engne at an rpm after the distributor has fully advanced, like at 4500 to 4800 rpms, and then 31 is probably a little too much. In order to find the exact amount for your car, you really need to put it on a dyno and try it as the modifcations that you have done will affect it.
Bye the way, that car is in ITC now.
Derek Ketchie