I made an adapter once for the floor jack to remove a F350 5 speed Transmission and Transfer Case (I should say I had a buddy make one and I helped) when I did a clutch replacement on it.

I don't have any pictures but what we did was took a pinion gear from a blown rear end and cut the gear section off of it. Took a piece of plate steel that was big enough to match up to the crossmember mount, cut a hole in the middle and welded the two together. Pulled the jack plate out, dropped the pinion in and used the nut and large washer to secure it to the jack. I was able to bolt the tranny and transfer case as one to the jack and move it around and jack it up into place under the truck.

I wish I had pictures, I have thought about using the jack for the same thing. Ended up buying the sears one, and did the SC-Longhair mod to it, and the bike is spending the winter on it.

DW

 

If you're going to fab some thing up... one of these wont take up much space.

 

I like this one. I would patten and sell if I was you!
I made up a 12" X 12" H shaped adaptor out of u-channel and welded a piece 1" bar stock in the middle that fits my floor jack, not the most stable but I put stands under it as soon as it is up