I've swapped an engine. If you have the tools and a garage I'd say it's not that difficult if you're technically minded at all. Just make sure you make notes of where everything goes before you take it apart.
I did it on the street in the dead of winter, which wasn't pleasant. Had to rent an engine crane too. But if you do undertake it I'll be willing to offer any advice you need.
Yes, your gearbox will fit.