Q: Retrieve old G4 drive data on newer iMac?

Yes, but you may find that the drives are read-only.

(135140)

Remember that G4 tower drives' interface were PATA, whereas most current enclosures are SATA. The most cost-effective solution is a USB univeral drive adaptor like this one:

http://eshop.macsales.com/item/NewerTech/U3NVSPATA/

It handles the older interfaces and the newer ones. The brand isn't important--this was to show the possibility. You may find a similar item cheaper on anther site; I posted the link because I've used that model to connect old PATA drives to a modern Mac and know it works.

I think it would. Most have two interfaces for PATA/IDE: a standard 40-pin connector for 3.5-inch drives and a separate one for 2.5-inch notebook drives.