Some time ago I got a nice Peacock G81 3000 case and the last week some G80-1502LQEDE-0s, so I decided to try to use a G80-1502 PCB with the G81 case.
If you look at a G80-1502
http://deskthority.net/wiki/Cherry_G80-1502
you can see what the problem is.
First the card reader, but I cutted the cable from it and leave the card reader in the old case.
The biggest issue is that a G80-1502 have a really big controller board.
It's much bigger than the controller board from a G80/81 3000.
After removing some of the inner plastic of the case the pcb fitted into the case.
The main PCB with the switches on it needed some cutting on the left and right side, because the PCB was longer than a G80 3000 PCB.
It was a pretty harsh mod, because I used only a metal shear to remove the plastic.
Maybe next time I use dremel, so its more clean.
At first only one picture from the result, later I add some pictures from the inner keyboard.

Feel free to ask questions.
Maybe someone had done something similar?