As promised, I have packaged this up for anyone to use. It now includes a compiled binary and the Xcode project.

I improved the code a little. Apparently 4MiB ROMs only compute the checksum for the first 3MiB. So those are working now, and just a few odds and ends that I tied up.

Grab it here if you wish:

http://www.d.umn.edu/~bold0070/MacROMChecksum1.0.zip