Sorry, I didn't notice where you're from. Perhaps mislead by the picture in the first post, when you said big deer, I was thinking big mule deer or big white tailed deer. 300 pounds on the hoof is a bruiser, take out 50 pounds for guts, so maybe 250 pounds maximum lift, more likely 200 or under. Most adult men, especially outdoorsmen, can do that unless there's some kind of physical disability or extreme age involved.
One option might be a barrel hoist. Another is what they call a "Tommy lift" .. hydraulic tailgate lift.
Thinkin' out loud here ... we mounted a base plate in the front of one of our pickup trucks, then wired a removable 4000 pound electric winch to it. We had an A-frame (arch) over the back of the bed. This was to lift logs so we could drag whole logs in as firewood rather than split and load individual blocks, but you could omit the a-frame, use a 2-3 2x12s 8 feet long as a ramp, and employ a small electric winch the same way.
Tom
