I am not a mechanical engineer, but looking at the third leg of that wonderful Bonneville side motor mount, it seems like the threaded rod is the main support linking it to the engine.

The spacer seems to just be there for the ride (literally). When the rod is removed, the spacer slides freely around its little area just above the balancer and compressor pulleys, though it still needs to be wrestled out.

I'm not about to remove the spacer and the threaded rod, and leave my engine sitting on two-thirds of a mount, but belt changes would be so much easier if it were removed, or even shortened by a quarter-inch. Thoughts?

Do not shorten it. Feel free to pull the stud and spacer w/o worries of the engine moving. I change the belt that way all the time. No problem pulling it.

You have no choice but to remove that spacer to change the belt. The SC belt goes threw the mount. Like Bill said, just remove the nut, then the stud, and finally the spacer. A few times I had to loosen the other two nuts and then the spacer comes right out. Be careful, the crank sensor wire is right there. You can always put a floor jack under the engine with a board to hold the engine up if your concerned about it. There is a write up about changing the SC belt in tech info and it explains how to remove that spacer.

Typically would loosen the nut a half turn, get the E torx onto the stud and pull it. (less turns on that nut = quicker)

Use a pick to undo the crank sensor, slide the spacer out. (you'll get really good at it if you swap the belt a couple times)

Do the belt and reverse..

Start car, see engine light, plug crank sensor back in.

Can't say I've ever forgot the crank sensor. But ya, make sure you unplug it, the spacer is real close and you risk damaging the wires.

I've never unplugged the crank sensor while changing the belt before. Good to know!

I've just always had to wrestle out the spacer after removing the nut and stud, and was wondering if there'* an easier way to get it in and out.

If I remember right, one side has a little angle on it to make it slide in easier. I've always cracked the other 2 nuts and then it'* easy.

Side of the spacer? Mine is perfectly flat on both sides.

Perhaps I'm thinking of something else.

I'll admit that I did not put the spacer on the water pump side of the engine and I never put the tans-engine bracket thing back on. (knock on wood) Nothing bad has happened so far.