I am using gimp-print 4.3.21. I have tried to configure it manually, I have tried configuring it using RH print manager, and I'v tried configuring using the web based CUPS manager. I'v even tried configuring it in RH print manager and then editing the files to change certain things.
I could not get gimp-print 4.3.21 to compile with foomatic either. I had to ues the --without-foomatic option in configure. I downloaded the two foomatic files and put them in my path but it still does not work. I configured gimp-print --with-cups though, in hope that maybe it would work.
The C64 driver is not included in older versions of gimp-print. You need 4.3.21 or 4.2.6-pre2. After installing gimp-print it was weird. The new drivers (including the C64 one) showed up in the webbased cups thing but NOT in the RH print manager.
I did the following things to configure it in the web based CUPS manager:
Step 1)
I set name, location and description
Step 2)
I selected "USB Printer 1 (Epson Stylus C64)"
Step 3)
I selected "Epson"
Step 4)
I selected "Epson Stylus C64 ....."
Looks like everything should work, restart CUPS but it still does not work

The only weird thing about that was that it set the device to something like "usb://Epson%20Stylus.....". Since this didn't look right and didn't work I tried changing the config to file so that the device was "/dev/usb/fd0". still didn't work. I also tried many many other combinations like that ("usb:/fd0","usb:/dev/fd0", etc.) but none worked.