1965 plymouth Barracuda 273 commando, switching from 9 1/4 to 10 and 1/2 clutch.

I don't know part numbers but maybe someone more knowledgable can contribute those. Any later small block bellhousing works as long as the opening for the transmission bearing retainer is 4.354". (OD tranny uses 5-1/8") Look for the casting number 2892482. Grab a fork form a 66 or newer B&E big block that is 10-7/8" OAL. Use the pivot from your existing bellhousing. You will have to modify a ball stud and bracket for the bellhousing to get alignment or Brewers Performance sells one(BSB636 I believe) Shorten your existing bellcrank or use a Brewers Performance TS636.
Have fiun!