What host bust adapator are you using? The 2 GB FCA2684 requires the FIBRE_SCSI TIMA kit on 7.3-x so I'll wager that you have a varient of of this controller to along with the nifty new EVA 3000.
Do you have access to an 8.2 boot CD? If so I'd do my clean install of 7.3-1 on a scratch scsi disk, load ECOs, then boot from the 8.2 kit and backup/image the new system disk.
If you want to move your current system disk, again boot from the 8.2 CD and use backup/image.
You will need to use wwidmgr to configure the new fibre channel disk as a boot device.
You could do a minimal boot at the console and use backup/image to move your system disk. Should be fine doesn't mean will be fine, but you could probably do this. Of course you'll still need to come up with boot media to restore your system disk backups if the need ever arises.
You also install the older 1gb hba, although I wouldn't recommend this option.
With all that, why not take this opportunity to install 8.2 or 7.3-2? VMS 7.3-1 is out of support, 7.3-2 will go into extended support if you're not ready to jump to 8.2 yet.
Andy
If you don't have time to do it right, when will you have time to do it over? Reach me at first_name + "." + last_name at sysmanager net