Depending on usage, that Tractor is going to be a bear. Like an old drag car, it's meant to go in a straight line and not much else.
Small Kubotas with shuttle shift or hydrostatic transmissions are light, powerful, and very very useful even in small spaces. Just thinking out loud here.
My old boat:
http://weeksmarine.com/robert.jpg
I was so in love with that boat, I used to polish the mains.... Could have done kidney surgery in that engineroom. I had the engines balanced perfectly, I turned them up to 2200rpms and they ran smooth as silk.
http://i68.photobucket.com/albums/i6...Detroit149.jpg