My buddy has a Samurai that he tows behind his RV; fun little car but I barely fit in the passenger seat and it sure feels like you're pedaling hard on the highway. He did take me off-road a little bit though and it seems pretty competent for such a little thing
Engine swaps can be a lot of fun, or not depending on how well it's planned and what the ultimate goals are. No doubt a blown 502 in the back of a VW bus is pretty cool but it definitely fails on the practicality side. Hanging around race tracks you get to see a lot of "alterations" from stock, plenty of folks who think they know better than the original engineers but very few who actually do.
The main thing for any modification regardless of how big or small is to be clear on what the goals are, otherwise you'll never know if you succeed or failed. Wanting more top end speed is pretty common among modifiers, I had a Triumph TR 4 that would scream at modern highway speeds so I definitely understand that. The original/factory solution was fitting an overdrive unit to the transmission, one common modification was swapping in a modern 5 speed unit. I never did either but probably would have if I still owned that car today.
In vintage car circles there's always disagreement between the purists and the modifiers. I'm firmly on the side of "it's your car, do whatever makes you happy." However, I've seen lots of mods that not only don't achieve what the person originally wanted but actually decrease the value, safety, or functionality of the ride in question.
Seeing the work the OP has already done I don't have any doubts he can pull off an engine swap. I would just encourage him to write down all the goals of doing so and also what the possible downsides are as well. Finally, look at ways to achieve some or all of the goals without swapping the engine (turbos come to mind).
JMHO,
John