tricky spot. (I still want my poorboy sammich)(and some smolich sausages plez) every time I see joliet I get hungry.
if it was me, i'd still keep it, i'd strip & sell the ski, make a decent profit, no losses... (or maybe try and get the seller to refund a couple hondo's after you tell him how complicated, ((and illegal)) he made this deal go down) especially if the title is in his name, and not just an open title.
in theory, you could maybe locate a valid plate and title for the right year, but that's really not recommended, just that i've heard of that done before.
see if you can squeeze the guy for a small refund, then part it out.
or... if you want it done right, ya, pull the correct VIN # if you can locate it, see if a title can be obtained for the correct vin, but in "theory" your also assuming the vin # you pull off the gas/oil tank is the original gas/oil tank as well, so you'll be 99% sure, but never 100%.
lots of good parts on a ski (have we decided this is a 97 at this point ?) the engine with compression = money, the MPEM = money, lots of misc parts = money. you can't lose out financially IMO by holding onto it, you'll probably make 70% profit.