You might give pertronix a call. They have a phone number posted at www.pertronix.com.
You said that your distributer was a used one. I just remembered that I had a similar problem on my boat when I bought it. It would start and run, and you could blip the throttle, but it wouldn't hold any RPMs above a couple of grand.
I pulled the HEI, and it was full of a gunky oil/dirt/water mixture. All of the advance mechanism was gummed and corroded up and would hardly move, so I wasn't getting the amount of advance the motor needed to run above and idle (it idled fine, like there was nothing wrong). Took it apart and cleaned everything thouroghly, and put a new module, coil, cap, and rotor in it. I put it back on the motor and it worked like a new distributer, no more rough running engine.
You might try looking and see if you have the same problem.
[ February 12, 2003, 08:41 PM: Message edited by: Sleek-Jet ]