I used to own the motorcycle encyclopedia till the early 90s and the most memorable engines where one of the two you mentioned. The other was the twin cyl 4 stroke Honda RC116
and get your heads round this:

21,500rpm.... no big deal

but 16 bhp !!!! from 50ccc is simply mindblogging

love that on my 28 speed racing bicycle for the local shops :)
(cop: "why arent you wearing a helmet and clocked at 150kmh?")


so if you multiply it for fun from 1966, 45 years later
we could have 100cc with 32hp, 200cc with 64hp

Of course its not that easy or possible but for sake of following
this "idealistic" formula keep going

500cc with 192hp and

1000cc with 384hp :)) - say the revvs go down to BMW s1000RR of 14,000
then probably 280hp would be closer.