I think a picture of this strange winch and the handle was posted here about 6mo-1yr ago... (search sometimes works, sometimes not so much)
IIRC, on the top of the winch had a round male ' 2 part key' and the handle fit over the key. (handle had a circle (round) end fitting over the key)
again, IIRC, its no longer made and the advise was to have a welder make one up.
(personally, I'd be looking for a deal on ebay for 2 winches)
what year was the boat made? I think the previous thread was on a 74-'76 venture ?