replacing a super 10 with an old transmission

Even if for some reason you had the smaller diameter, you could replace that with a larger shaft.

If it were me I would put a new pilot bearing in and check the shaft and forks and cross shaft bushings.

And again, if it were me I wouldn't put in a clutch that's been sitting for 20 years unless it is a yard truck. I would drain it and make sure there's no water in it and nothing on the plug, and I would replace the rear main seal and the rear seal on the transmission. And maybe the filter regulator also and maybe even the slave valve since it's been sitting for so long. And resurface the flywheel if needed and definitely a new flywheel bearing.

Hoses and such are much easier to change while the transmission is on the floor.

 

If you put it in as a 9 speed the driveshaft will be to short.