I usually don't recommend scissor hoists but for your situation a scissor is easier to mount but you will end up with alot of extra weight that takes away payload.
Venco makes one of the better hoists you can get one with a subrame and hinges all you need to do is remove the deck mount the hoist frame to the truck bolt or weld the hinges to the deck and mount the lift arms to the long sills of the deck. Now the second issue you will have is the long sills what the crossmembers sit on my not be deep enough. A welding shop may have to modify the long sills to make it work. For a scissor hoist you need minimum 5 inch sills. Another thing to consider is strengthening up the deck.