[aerohead]

A neighbor had a 2-cyl VW aircraft conversion we were considering for a model to do a 2-banger to share between his Bug and my Ghia.
He died,and that was the end of that.
In the intervening years I've come to believe that the reserve power of the original engine is an important safety factor,as some emergencies require judicious use of horsepower when braking won't save you from the situation (as with motorcycles).
Passing and hill climbing will suffer immediately,and any acceleration will require longer residence time in transitory engine operation which is the least efficient in BSFC.
My 60-bhp CRX already has head-wind issues on flat highways,requiring downshifts to a higher friction lower gear.
Taking a more massive vehicle of greater frontal area to a lower hp than that of the Honda might be a recipe for disappointment.
I think you'd regret the change.
And there are dozens and dozens of vehicles which without any mods,would deliver like safety,comfort,etc.,and with higher efficiency.