Sounds like you need to drop back ten and punt. I don't know exact interchange information but.......
I would place the 2 transmissions side by side and compare carefully things like the pilot bearing size, spline count and length, the fork etc. Maybe you need the flywheel and clutch from the other engine. Or maybe the bellhousing and fork from the old trans. I'm also pretty sure a junkyard can tell you if they can interchange.
Or Marlin probably just knows what you need right off the top of his head. :thumb: