There's really no need to low level format it on the iMac. You just need to format it on the Plus. Ideally what you need is a set of System 6.0.8 installer floppies, and one of them needs to contain a good hard drive formatting utility, and a SCSI Zip drive and one Zip disk. That's all. Those items alone will allow you to install an operating system and boot to it.
If you can score a Zip drive, a disk, and some floppies, I'd be happy to build a 6.0.8 install set and a Plus Zip boot disk for you. I just got a Plus today and set it up just like you want to so I can test it before sending your disks back.