They aren't all the same. You need the C6 Corvette engine mount brackets, part numbers 10349964 and 10349965.
The engine mount crossbar that comes with the kit bolts directly to the engine mount brackets.
I had the same problem. I put a set of washers under the motor mount brackets on each side to push them out a little and then everything lined up.
I'm using the original mounting setup (aluminum beam and mounts welded directly into frame) and my driver side was fine but the passenger was 1/2'' off so I just slotted the engine mount. I had the same fitment issue with my plastic mockup block as well *shrug*