no, not Mcguyver, just a Mechanical Engineer who does some fatigue analysis, so I know a little about crack propagation, stress concentrators, notch factors, etc.

and in this type of loading, the primary load on the input shaft will be torsion, not shear or bending. the material in the center will have very little impact on torsional strength of a shaft, so I would not expect a solid input shaft to be significantly stronger than a hollow one.

I had the 904 out of my 5th ave that I sold to a guy north of detroit, he was just going to cannibalize the gearsets to put them into a non lockup 904, so he probably has in input shaft. unfortunately I don't think I still have his contact info...

I'd suggest putting a wanted ad up in the classifieds here, or over at the dippy.org forum, lots of F/M/J dudes there that could probably help you out...or just pick up a whole spare tranny out of a 5th ave in a JY....