Hello Chris,   still working on my 77 RC.  The steering u-joints are very lose.  I can't find any new exact replacements, but a couple of places have these:

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Universal Joint, Steering - Complete U-joint. Has 7\8&quot; round ends. Comes with pins and grease zerk. For models: 66, Super 66, 77, Super 77, 88, Super 88, 660, 770, 880. Replaces KA758. (Part No: USJ78)
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(This is a blurb from Yesterday's Tractors.)

I bought one of these and it looks promising but:

-- it's about 1/4 inch shorter than original

-- it requires a hole through the shaft, not the bolt groove plus woodruff key of the original.

Looks like I could make it work either by drilling through the shafts for the new bolts or having it welded to the shafts. 

I would have to install each shaft about 1/8&quot; less than before to make up for the shorter u-joint.

Does this sound like the way to go?   Any different suggestions? 

Thanks as always.

Tom