You're correct. All I was saying is that if you're hooked to a timed vacuum port, you shouldn't have timing jumping around unless it's picking up a vacuum signal or the mech advance is spinning up a little too soon.
I also have the Trailbeast HEI conversion kit--worked well on my Scamp. My 5.2 has a stock dizzy; I never got a chance to really tinker with the advance curve, despite my desire to...
Tim's correct though--you might need to curve the distributor. There are some threads about that in the SB tech section also...but with the timing will come some possible need for tinkering with the carb also...idle settings, mixture, pump shot, etc. Speaking of that, with the off idle hesitation, you may need to mess around with the pump cam or squirter size.