Of course we can't judge the mechanical condition of these GRAVELY attachments from a pic. Not to slam louis-8, but IMO they're worth very substantially more than "$100.00" & you may have a 3rd GRAVELY attachment-a complete front PTO system.
Note that part of a front PTO is connected to the MA-600 40" deck. These heavy duty mowers are sought after & in good condition often command $200-$250. They're especially useful on a walk behind 12 hp, where they attach directly, w/o that '4 bolt' front PTO part.
The snow blower has got to be popular in NH. I can't tell from pic what's going on w/the chute, looks short, like the adjustable top piece might be off it. Also can't tell from the pic if the blower is dedicated to riders, exclusive their front mount, or another adapted '4 bolt' walk behind attachment? I'd suggest you take stock of what front PTO components you have, might want to keep them together. In good condition the blower may be another $200-$250 item. A complete front PTO system alone may be worth $200.
The pic hungry crowd, might respond to a quick cleaning & coat of GRAVELY red paint. Your attachments will appear shiney & new, even if rusty & broken. Could easily boost their "worth". Also try to fill the frame w/the attachments.