I have a 258 w/ an HEI, so my points may not be entirely relevant, but there were two issues that had to be addressed that I think are worth sharing.
1. Had to swap out to a amc v-8 dizzy drive gear (reverse cut when compared to stock chevy drive gear)
2. I had to file the end of the shaft a wee bit because of the way it seated in the oil pump. This involved filing the fillets back about 1/16", not the length of the shaft. In other words, you make the flat screwdriver end a little longer by filing shaft itself, not the end. The fillets were hitting on my oil pump when engaged and not allowing the distributor clamp portion to touch down on the block. Cost me a distributor before I got this figured out because I overclamped it and broke the seating portion off my dizzy casting.....d'oh. Plus I could not hold timing because the clamp portion would not seat. I tried all sorts of stuff before I figured that one out.
Hope this helps.