Gary,
From what I've read, if your mac supports Cable Select(and you indicated it did) you're okay...your computer selects Master and Slave based on which Drive is connected to which connector...My G4(a Digital Audio, G4/466) does not support Cable Select, so when I added a Maxtor drive, I left the IBM drive as Master and made the Maxtor drive the Slave...I don't think it makes any difference which is which.
If your G4 manual said to use Cable Select, that's what I'd use.
Just my 2 cents,
Clay