Did you remember to install the roll pin that holds that "block" to the shaft rail. The block being the one that the shifter sits in?
There's also a couple of roll pins involved with mounting the shift forks to the shaft.
Do the gears grind, or ???
I fiqured this was obvious, but I'll mention it anyway, but is it just a case of the shifter hitting something, now that the crossmember is in place?