In case anyone down the line has the same question...
The G4 17" FP iMac case fan is a standard 92mm. The connector is a 3 pin bayonnet (inside a plastic connector) from the fan, but only two wires actually connect to the mobo (red & black). The generic fan I had planned to replace the original fan fit fine, but I couldn't make the connectors work, so I settled for cleaning and re-installing the original fan - with the fan cleanup and the blowout of the dust from the case, the machine is at least a bit quieter than it was previously. I may yet spring for a pricey ultra quiet fan if the nosie gets to be too much.
Cracking the case was not as daunting as I had been led to believe. I also swapped the stock 80GB HD with a 320GB WD EIDE drive and swapped the 256MB factory RAM with a 1GB stick. Even though apple claims the iMac only takes 512MB per slot, the 1 GB stick is recognized and active, bringing me to 1.5 GB. The HD is recognized and working fine.
Hopefully I can stretch this machine out for another year or so before caving in to an all-new system.