Extension for 400kB MFS disk support?

[hjalfi]

I have a PowerBook 150. I want to be able to format and use 400kB MFS disks, which it doesn't support. (For testing creation of MFS disks with FluxEngine.)

My understanding is that 400kB disks are physically the same as 800kB disks, just single-sided and with a different filesystem, so adding support ought to be a simple software matter. Does such an extension already exist?