Which 440 to buy?

What I would go for and what you intend to do is totally different.
I would buy the $450 engine and go through it and rebuild my own transmission.
The engine and transmission are cores if unproven.

For your intentions, the motorhome engine sounds like what you want.
As long as you hear it run before pulling, and verify good oil pressure etc.
2 grand seems like a lot though.
And the transmission will have to be opened up to change the tail shaft etc. so there's extra cost and work there.

Let us know what you decide...