Was the microdrive fully implemented in fuse?
Update:
Ok so the problem I was having is that fuse is not really fuse in pacman .. its fuse-emulator

after that it was all peachy - for the curious the roms are in /usr/share/fuse but yaourt & pacman see the package as fuse-emulator.
So loaded the if1-2.rom and seems to be working fine.
One followup question - is there a utility or a way I can get fuse to generate microdrives with data from the PC? What I want to do is assemble a bin file and create a micrdrive similar to what pasmo does with --tapbas /tzxbas.