I'm a cheap bastard and trying to build a driveshaft in the likewise fashion. I have a piece of 2.5" DOM (63.5mm OD) and need it to fit in a hole 61mm wide.

That is removing 2.5mm from the OD. Think this can be done with sanding or am I crazy to try anything but a machinist's lathe?

I was thinking careful sanding with a flap disc then maybe dropping it into som ice water, while I heat the other thing with a torch and get it cherry red. Might be enough to slip it right in.

other way around, the shaft goes over the yoke or splined shaft.

other way around, the shaft goes over the yoke or splined shaft.

I hear ya, but my plan was to slip the new tubing into the end of the old tubing and weld. I don't have a chopsaw or lathe to cut off the old tubing cleanly from the yoke end.

then I'd get a larger piece so the middle slides over the ends. If you try to cut that tube on anything but a lathe, you'll never be sure on concentricity. If your shaft isn't straight, it'll wobble and eat Ujoints constantly.