Hello lisalist,
For now, disk media type is controlled by source code configuration options, and (unlike e.g. whatever code bootloads BLU) you will need separate builds of the bootloader for Twiggys and for 3.5" disks.
Fortunately, bootloader binaries for both types are available at the github repo, along with a Python utility program that builds bootable .dc42 disk images.
Bootloaders are not so interesting, so for the sake of having something to look at, here is a Lisa running a (boring) test program generated by
another Python utility available in the repository.
I hope this is useful,
--Tom