Well, I just cant leave well enough alone:
I was looking at pictures of the 14u32 and the 14u34/64.
It appears they use the same housings. I got a hold of some high res pics of the 14U32 and sure enough: where the 4th tensioner would go is a removable block off plate.
The rest of the differences just look like thread guide loops and a screw on thread spool holder. A few other differences that make no difference to function (like a different handle, etc)
Even the needle holder looks the same as the 4 thread version.
So, I ordered up a spare tensioner assembly and I'll see if the 3 thread Ultralock is just a few parts away from being a 4 thread.
My missus thinks I'm crazy.....but I just can't stop tinkering with stuff!
Besides, it was only 20 bucks. What have I got to loose?