If you have not already done so, create the Backup Edge boot diskettes.
Then remove the system drive, and install the new blank drive with the same SCSI ID and termination settings.
Boot from the diskettes that you have made, follow the instructions on configuring a new hard drive, and restore the data from the tape.
All told it should take about 2 hours.
And your original hard drive is still safe (or as safe as it can be.)