Try this - I haven’t with 1.4 ROMs but am curious:
Rename the boot partitions (WB_2.x and WB_1.3) using HDToolbox. Make a backup first, just in case.
Create a new partition DH0 with the highest boot priority. Install a program to load a kickstart (don’t know what works with the 060 - I haven’t finished building my A3660 l), similar to SetCPU (68020+68851/68030 only) or Set040 (68040 only? Or is the 68060 MMU close enough).
Anyway you get the idea. You can create a startup sequence (use 1.3 or 1.4 CLI commands - 2.0 commands tend to crash under 1.4) that asks you which OS you want to boot. You then run the Kickstart loading program to load 1.3, 2.0,3.1, whatever. Check in the startup-sequence what OS is running, reassign c:, devs:, SYS:, l:, etc to the appropriate partition and execute the startup-sequence on that partition.
The above assumes that 1.4 does not crash with the 68060 (quite possible) and you may have to click the hidden gadget on the 1.4 Kickstart selection screen to get this going.
The part below is verified working - one of my A2000s is doing exactly this:
The above still works with minor variations if you have Kickstart 3.1.4 installed. (I.e no need to rename partition a to defeat 1.4’s autobooting, no need to use 1.3 or 1.4 CLI commands, 3.1 or 3.1.4 will do)
Always boot from the 3.1/3.1.4 partition, load other kickstart as needed, reboot, detect other Kickstart version is running and then reassign/transfer to the correct partition If needed using CLI commands.
Btw the 68040 is not really supported under 1.3 and for the 68060 (assuming full with FPU and MMU), you’d need to patch the other Kickstart so that it knows what to do with the FPU stack frame. If you get 1.3 working with a full 68060: let us know.