I'm guessing it should be like 2.04, so there should be a Monitors drawer inside Workbench. If it's not there it may have been accidentally dragged into one of the other drawers. Failing that, copy it over from one of the 2.05 OS disks. As for adding monitors, all you should need to do is drag which ever ones you want into the Monitor drawer and they will be ready to use by Prefs after a reboot. Or, just double click the monitor driver wherever it is to test it out with Prefs in that session.
I have no idea why, but the disk I have does not have the monitors in the Monitor Store drawer or the Monitor drawer. Anyway I went on the hunt and pulled out the original disks and you are correct there should be a Monitor drawer and Monitor Store drawer. Inside the Monitor store drawer there is the Multiscan, plus two others. So I just placed them in the Monitor drawer and rebooted and they are there working for me.
Little tip, do not try to use the monitors from the OS3 disk. That would be bad. I did that and then the 600 refused to boot. Instead it filled the screen with scrolling load errors.. Endless.
My problem with 2.05 is that the procedure for setting up monitors and datatypes isn't that clear. I try to fire up a simple picture in DOpus and it states that can't support the screen mode or something. They are IFF images. I'll sort it but looks like 2.1 would be the answer. I could simply copy the drawers and files over, but I think I'll wait till I can get hold of a 2.1 install disk and then I can set up the DEVS drawer. Need that so bad.