Wow 60 HP from 250cc has got to be some record ?
I've had three four cylinder motorcycle , and don't ever want another one.
The ones I've had were two Hondas (500 and a 750) and one Kawasaki (750).
They all had two things in common.
First those carbs ! getting them timed is no problem but keeping fuel flowing through all those little jets was a problem.
Second and more problematic is that :
They had the cam chain in the middle . So running more cams tends to wear the chain out faster. Also the replacement of said cam chain is a pain in the shop ! I'll take a single cylinder anytime.
I can just imagine the tiny size jets and of having 6 tiny carbs with gas drying in the jets overnight.

Still , it was an engineering marvel !