I have shimmed mine on a civy 350 HEI. You can put ring and pinion contact paste on the driven gear and install it and rotate. Push down on the top rotor mount to start and see where it walks to. Read the pattern and see if it the wear is causing the contact to wander towards the end of the tooth away from ideal center. Shim accordingly.
I know you already have a dizzy Gimp, but does pertronix make a replacement? I put one on on the exwifes GTO and it made a big difference. HEI would make more spark though.
Liz, covid, murdered 10/19/21