That would be so much easier if it was made on a machine supporting older kickstarts such as the A2000... just install a kickstart switch and make a cleaver startup sequence that feel the kickstart version and boot the correct WB accordingly to that.
With the A1200 it's a bigger problem... on my old machine I had the startupsequence boot into clean CLI if I pressed right button during boot or start ReloKick if I pressed left button during boot, but that's childsplay compared to what you want.
A thought... have OS3.9 installed on a HD on the internal IDE controller, have startup sequence feel for pressed and let BlizKick load 2.0 or 1.3 depending on what button is pressed (if any). Then setup a HD on the SCSI controller to feel for kickstart version and boot the correct WB according to that.
There's probably other ways of doing it but it's late at night and I'm out of ideas.
