sk7

Do you know what the dimensions of your 600 are?
I think the shaft size is the same for the 500 and 600 so the gears should fit, but the mounting holes would be the problem.
Then again the motor mounts for the SH are slotted so it may not matter.
The original motors were coined as 550's, basically a 600, so I might be weary of using the 500BB.
There should be plenty of room as you noted.