3-2 shift, What's broken?
 

So, I'm in the process of breaking in my new engine. I was driving, with a bit of throttle, definitely not more than half. I shifted, from 3rd to 2nd gear because of the stupid stock shifter. I believe I shifted at about 4000rpms in 3rd gear, definitely not more than 5000. When I let out the clutch, my rear locked up and I got some pretty bad hop. I did not see the revs go over 6k, but I was kinda freaking out because I've never missed a shift and gone into the wrong gear before.

Now, when I try and accelerate, I get a TERRIBLE vibration above around 2000 rpms. The whole car shakes. I get the same vibration when leaving in first gear. The only way to eliminate the vibration is to keep RPMs low and very slowly let out the clutch. I discovered after a little more investigation that this vibration appears to be my driveshaft rubbing against my safety loop. Is it possible to break a poly trans mount and an engine mount? I realized that the rubbing goes away at engine decel. I don't have time to jack it up and take a look until this weekend at the earliest.

Has anyone broken anything like this by missing a shift before?

The trans was built to handle 800+hp, I have a moser 12 bolt, and the clutch is a McLeod original twin.

I would have to agree with you, if that happened to me the first thing I would check out would be the clutch.

A missed shift from 3 to 2 will bend the floater plate tabs. It can be repaired and beefed up with a thicker tab.

If the vibration is consistent with rpm rather than speed I would think that the issue is possibly the clutch or even a bent input shaft.

I updated the first post. Seems to be the driveshaft rubbing against my safety loop. Anyone have a problem like this before?