Tongue weight rating matters more than towing limit.

There are lots of really poorly designed hitch accessories out there so don't believe what some of them say.

Why are you not just putting it in the vehicle?

. . . And securely tie it down as I've seen the result of an engine that was not tied down in the bed of a pickup. Engine sitting at the tail gate end of bed, truck hits something, front end of truck compresses enough that dash comes forward towards driver , loose engine then hits back of cab bending it causing the seat to be pushed forward.