A few months ago I put in a MU-13-1. 25 Con O. That clutch adapts the bigger 13 in clutch onto the stock 1 1/4 input shaft. SBC has great customer service too. I think I'd go with the Con OFE if I was to do it again (just a few hundred dollars more).
Might consider replacing the input shaft with a 1 3/8 and then later you have the same clutch/fly wheel to swap out a NV5600... if my thinking is right. Especially if you are pondering an NV5600 swap later... I have considered this swap. Also might think about fixing the 5th gear nut with a bigger shaft. All these things add quite a bit of cost and effort to the job and can be done later (5thh gear nut I mean) but something to ponder.
Other things to consider: I'd consider putting in SBC,s master/slave hydraulic cylinder while your at it. I'd also recommend replacing the rear crank seal and input shaft seal to avoid any leaks into the new clutch. I also replaced the tailshaft rear seal- real easy job. Also replace the clutch arm pivot ball with spring (About $20). All these extra jobs were real easy and first time for me. I got the parts (by SBC recommendation) from Blumenfals (Spell?) transmission and they were cheap.
When you get closer to getting it done, I can tell you what not to do on this clutch job. Actually, quite a few things not to do. That transmission is real heavy so you definately want a helper to man handle that thing in and out.
If I could do this job you can too.
Good luck,
Dave
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