I'd recommend reading some users' experiences with these cranes. From what I've gathered, 1000 Lbs is EXTREMELY optimistic, especially if considering any of the offerings from Harbor Freight. The realistic rating is more like about 500 Lbs max. If you get one that has a swivel base, about 200-300 Lbs and it starts getting difficult to rotate the base. Anway, here's the link:
Truck Hoist/Crane
It looks like you could probably lift an engine into the bed of your truck, but it sounds iffy about whether you could do it with the transmission attached.