It's actually pretty simple. The pressure plate has to fit the flywheel. The clutch disk has to fit the transmission input shaft. The clutch disk needs to be the same diameter or smaller than the pressure plate diameter.

The throwout bearing either has to fit the sleeve around the input shaft, or else it's a hydraulic one-piece that bolts to the front of the transmission. You need to know if the throwout bearing is large enough diameter to catch the fingers on the pressure plate. Most are. There is also some variation in length of the throwout bearing carrier or holder.

Here's an example....I collect cheap parts. The goal was new clutch in my '64Dog D100. Stock clutch was an 11" Borg & Beck. Stock input shaft was 10 spline 1 1/8". I determined that the Borg & Beck and the diaphragm type used the same bolt pattern, and that an 11" OR a 12" pressure plate used the same holes on the flywheel. After searching for a while I bought a 12" Borg & Beck pressure plate brand new for a few dollars. I then bought an 11.5" clutch disk that had 10 x 1 1/8" splines. I bought a new bearing for my throwout after making sure the old one would cover all the ends of the lever tips. No problem. Drive off the old bearing and install new one.

I needed a pilot bearing because my crank was from an automatic transmission car, '86 Fifth Avenue. I found the late '90s Ram pilot bearing on Rockauto, although every part store in town had one as well. That's the one that drives into the torque converter ring. I test fit and there was a deep enough hole in the end of the crank that it'd all bolt together without any cutting or drilling. So I put it together. Done.

On my '77ford F150 I had bought a 12" set (barely used)because my truck had the 400 engine, the 12" was standard on it. Much to my surprise the truck had been rebuilt with a 400 crank but was originally a 351M...that had an 11" clutch. I didn't have an 11" disk, so I took the flywheel and pressure plate to a machine shop and for $35 they drilled new holes for the 12" pressure plate. End of story.

In your situation, you are having trouble finding a pilot bearing that fits inside the torque converter ring, but has the right ID for the transmission input shaft. So here's what you do...
Find a roller pilot bearing for your transmission input shaft. Get a pilot bearing for the Mopar engine like I used, the '90s Ram pickup. It is a small bearing inside a large disk that serves as a spacer. Have a machine shop make a spacer to fit inside the TC ring and have the pilot bearing be a press fit into the spacer. The Ram pilot bearing may be useful as it is the right OD, it illustrates the remedy, and it may be usable in fabricating the spacer. But at the very least it'll point the machinist in the right direction.

More Specifically, you buy the National FC69007 that fits your crankshaft. Then you buy either the National 57080 and bore the 69007 out to press fit the smaller bearing into it, or else you buy the SKF 6302VSP43 and bore the 69007 out to fit it. You are basically creating a spacer for the correct bearing for your transmission input shaft.

R.