I took my old AO 820 disposable knife holder, that slides onto the runners
of an 820 rotary (these came out 15 or more years ago, should still be
floating around with used equipment dealers) and slide this into the
slot of cryostat 855 Histocut.  You can use any high profile disposable
knife, no problems, perfect fit, excellent reuse of an old disposable knife
holder.  There is no antiroll device, but I use brush technic anyway.

Got rid of the sidearm knife holder (finger guillotine!) without batting
an eyelash.  If worse comes to worse, an 820 knife holder with all the
screws, knife elevating devices, for c profile steel knives,etc might
work, and use a disposable knife holder that slides in like a c profile
blade.  Probably needs to be an 820 recycled holder, like the disposable
holder.

Good luck, someone may have one to sell, maybe give away???

Gayle Callis