Thank you very much for the advice Thomas. I am going to check and double check this whole procedure and try again tonight using all your info!
I'm just wondering now how I managed to install my other a1200's 12GB internal IDE HD and 20GB external SCSI HD...both using partitions upto 6GB!? I seem to remember installing the PFS Direct SCSI file sytem as you suggested above...because it supported TD64 (or whatever it's called). But I can't remember updating the scsi.device. Oh well, I guess I must have at some point!
One more thing, can you explain to me why these 4GB> partitions of the HD work fine in WinUAE but not on my real Amiga? Is WinUAE bypassing the system directory scsi.device functions, or something?