I haven't noticed a difference in road tripping performance between totally empty and fully loaded with cargo a grown adult in every seat, so I doubt adding ~75-150 pounds of bumper to the back is suddenly going to make it intolerable. Made it up multiple mountain passes on pavement, and all sorts of steep trails on gravel. Definitely not a good enough reason to justify an engine swap on its own.
That all changes if you're already having trouble on hills without cargo or passengers. If it's having a lot of trouble doing what you want right now, then maybe that 350 wouldn't be such a bad idea. If you like how it drives at the moment, leave that 2F alone until you've started adding more armor and can re-assess.