I was just guessing 8 hp considering the trailing mowing machines on the market are using 5 hp Honda’s to power a 7′ sickle bar.
I have a 8hp Honda I pulled off a snow blower that was scraped and use it for my wood splitter. Way more power than I need but it was free and in excellent condition.
The Elmo Reed hitch cart had an engine that bolted as a unit (pto/engine/various neccessaties) in a cage format so if you didn’t need the engine with four bolts it could be lowered to the ground and the cart backed over it and out of the way.