Building it on top of ProDOS might be fairly doable.
ProDOS provides an API for block-based file I/O that's fairly simple and supports multiple different drive types. On a 128k system you'd get a 64k RAM disk for free. It might fit nicely with the current code.
And ProDOS already lives in the bank-switched Language Card area, so there would be good chunk of main RAM to work with, a little under 46K from $0800 to $BF00.
ProDOS provides an API for block-based file I/O that's fairly simple and supports multiple different drive types. On a 128k system you'd get a 64k RAM disk for free. It might fit nicely with the current code.
And ProDOS already lives in the bank-switched Language Card area, so there would be good chunk of main RAM to work with, a little under 46K from $0800 to $BF00.