HEI conversion 250 distributor gear problem

[bretcopsey]

This project just keeps snowballing. Decided to convert the 250 in-line six cylinder to HEI distributor. Picked up a distributor at Advanced Auto for a 1975 Camaro. I got the wiring replaced all the way back to the junction block on the firewall, and just pulled out the original distributor. The distributor gear on the original compared to the HEI unit are reverse from one another. At first I thought I could just swap out the gears, however the original is about 1/8-3/16 of an inch shorter than the new one. This leaves excessive slop in the distributor shaft, and I'm not sure that I should try to make it up with shims. Any quick fixes for this?