I believe the pressure plate bolt pattern for the 12" clutch is on a wider radius than the 11", but if you can find a flywheel that's drilled for it that's the one to use. That extra 1/2" of facing material radius and the bigger pressure plate makes it much more effective if you're doing real truck stuff. Don't use a flywheel for a small block 400- - - -it is off balance to compensate for the longer stroke crankshaft and it will make a 350 vibrate.

Here's a complete kit- - - -flywheel, clutch, pressure plate, and accessories:

https://www.ebay.com/itm/133795601787?

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!