I too, used to do macro sections of prostate.  If I only knew then what I
know now...
Microm (newest division of Richard Allen Scientific, formerly associated with
Zeiss) distributes the Macro-flow cassette with disposable mold.  These
cassettes can be embedded just like the smaller cassettes and can be mounted
in a microtome with the standard jaw clamp.  The cassette orientation is then
rotated 90 degrees and be sectioned normally. The microtome must have a
vertical stroke of 64 mm (Microm microtomes have this clearance)
Dawn M. Truscott, HT(ASCP)
Microm Division of RAS