Are all the bravo's , 1.X,XZ, and XR the same length (crank shaft to prop shaft) so, for example, if I set my X at 17" and mount a bravo 1 then switch to an XR is my prop at the same height?

Yes.

are there any alternatives to IMCO to obtain a shorter bravo style drive?

Somebody on the board was working on shortening a Bravo lower a while back, but the last I saw it was still in the testing stage. I don't know what happened when it went into testing.
There aren't any other manufacturers other than Imco that I'm aware of.