You're going to encounter an extremely close fit between the big distributor housing and the firewall. Be sure the motor mounts are in "as new" condition or you'll break distributor caps frequently from torque reaction. The housing length and the interface with the oil pump drive is identical to the point type distributor- - - -no problems there. A late 1980's electronic advance HEI distributor will not work- - - -be sure to get one with a vacuum advance on it. Rebuild the flyweights and bushings in the centrifugal advance and make sure there's no lost motion- - - -they're notorious for wearing out the pivot pins for the weights. The old style distributor for the point type system with the window in the cap for adjusting the points can be converted to work with the HEI pickup coil and reluctor components, but the module needs to be mounted remotely on a heat sink. I have a system like that in the process of being converted, as well as an original stovebolt six distributor that's getting the same kind of modifications. It takes some machining to the breaker plate for a pivoted vacuum advance for the pickup, and a pointed steel plate mounted onto the rotating cam to trigger the pickup coil. The end result will be a stock-appearing distributor with hidden electronic components.

If you're running a cast iron camshaft, the bronze gear isn't necessary. The original gear will work OK unless you're also running a roller cam with a steel core.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!