I am sorry I came late to this thread but I wanted to add a few things that may have not been covered. The clearance between the gear bottom and the block is a min. .005. This is supposed to be checked with no cam gear or cam in place. You hold down on the housing and reach inside and lift up on the gear. I just bought a spare roller engine and tore it apart and decided to check the clearance. Someone had put in a non-roller dist. with the wrong cast gear that was wearing. But the clearance was correct.
There is a lot of focus on the gear material but there are additional causes even with the correct gear. The correct clearance is to allow the gear to come down to ride on the block for proper mesh with the cam. After-market distributors may not be drilled and pinned in the right location to allow this, and may require re-drilling. Another issue is computer distributors often have a longer shaft that engages with the
oil pump rod. Sometimes they bottom out against each other, not allowing the distributor to come down to it's proper location.
Another big issue now days is the High Volume pumps used in the SB. Comp Cams has warned about this and I seem to remember one of the cam companies refusing to warranty cams when a HV pump is used. We have all seen SB pump rods twisting off for various reasons. So a lot of guys put on the ARP better pump rod, which is a good idea. But consider, with a HV pump if you have stock
oil clearances that pump is going to put a greater strain on that distributor gear and reasonably cause greater wear. I just don't put in the HV pumps in the SB for that reason. It's not worth ruining the engine for.