Does anyone know for sure what the diameter is of the Merc/GM HEI distributor shaft w/ an external coil is?? (2000 502 MPI) I found a few posts here that say its .491". According to a GM parts site (Pace Performance), the small HEI cap w/ ext. coil is .428"

.491 that .428 has to be a misprint...now thats a GM, merc I don't know..Rob

I'm not so sure it's a mistake- I took off the distributor gear and measured the shaft with the only thing I had handy- a cheap plastic caliper. It's only graduated in 1/16ths and it measured not quite 7/16" in diameter. .428 is just a little over 13/32". . .

GM made both. The engine you have does have a .428 diameter shaft. Do you need a gear? If so, Scoggins-Dickey is probably your best bet.
Eddie

damn, never heard or saw that size, and none of the main manufactures makes bronze gears that I see in that dia.

Rather than use bronze, I ordered hardened steel: it's called a Melonized coating and is indicated for steel billet cams. Summit and Jeg's both sell them although I'm not sure in what sizes. I ordered mine from www.paceperformance.com

Neither Jegs or Summit carry the gear in .428. I've looked before, since they are so easy to order from. Jim Pace has a great parts dept. to order from.

I've ordered a few things from Pace as well. Good prices and shipped fast.

Crane sells a bronze one too. I believe it's actually .427"