The TBI distributors ALREADY have a melonized gear.There are tons of melonized gears at Pull-A-Part on Vortec distributors. It's a five-minute swap while you have the distributor out. I put one on my TBI distributor since I'm running a roller cam.
I went through this twenty years ago when I stuffed a '92 Caprice TBI roller-cam service-replacement "crate" long-block into my '88 K1500 TBI (flat-tappet cam) truck. I bought the crate engine from Pace Performance. They sold me a melonized distributor gear along with it because of the roller cam in the replacement engine.
The gear was for the larger distributor shaft of the coil-in-cap HEI--0.491 instead of the skinny-shaft TBI distributor (which might be 0.430 diameter?) So I call them and ask about getting a melonized gear for the skinny-shaft TBI distributor. The guy researches it for awhile, then tells me to use the distributor gear already on the distributor since the TBI distributor gears are all melonized.
I never did get a refund for the too-big gear they sold me.