Check the DISK ASIC JR revision on boot (or look at the label of the chip at U29. If it is "AB" revision then you can simply swap the ROMs from your dead Grid board into the Cruis'n Exotica board and all will work. However, if the board is a "A8" revision you'll notice that the ROM check fails on startup and it won't work. If you have some spare M27C160 ROMs (you can use U10/U11 from the Exotica board if you have a EPROM eraser) you can modify the 1.20 version of The Grid to run on the older "A8" revision boards.
First, grab the 1.20 revision U10, U11, U12 and U13 ROM images either from MAME or by dumping them from your own game ROMs using a ROM burner. Next, open up the U10 file in a hex editor and change the following bytes:
- Offset 0x7FFDA: Change 06 to 04
- Offset 0x7FFDC: Change B8 to BA
Now, save that ROM. Next, concatenate that file and U12, so that all the bytes of the modified U10 come first and all the bytes of U12 come second. Do the same with U11 and U13, making sure that all bytes of U11 come first and U13 come second. Now, burn the concatenated U10+U12 file to a M27C160 and insert it into the U10 slot. Do the same with the U11+U13 file and insert it into the U11 slot. Leave U12/U13 empty. Now, move U18 to the U14 slot. Move U19 to the U15 slot. Move U20 into the U16 slot. Finally, move U21 into the U17 slot. Leave all other ROMs and the PIC in the same location as they are labelled.
If you did everything right, the game will pass the ROM checks and start up just fine. For reference, your board should look something like
this.