You could try using manifold vacuum instead of ported & tuning it that way. Put vac adv on the drivers (manifold) port & setting initial with the vac gauge method (max vac then back off 1" in hg) & as you know on manifold the can will be maxed at idle. then shorten the slots for 35 total with the can capped. then adj springs for WOT then hookup/adj the can for part throttle high rpm/around town as previously described. You have nothing to lose at this point & if it dont work to your satisfaction then we can continue on in a different direction. EDIT 36-38 rather than 35 total with vac capped (I forgot we are working with a BB) and if it's a low compression 383 I'd suggest 38