Chrono Cross PS1 Memory Card Checksum

[Spamzilla]

I'm having an issue with trying to hack a PS1 memory card save checksum. The game is Chrono Cross and the format is .MCS from the pSX emulator. I have provided two files to illustrate the issue. The only difference between them is address 0x13E7 and the last four bytes which are probably the checksum. It isn't a Checksum-32 or any other common checksum that I know of. I ran it through a web-based checksum fixer but I would rather just write my own editor program than use that one.