Differences between earlier /6 engines and newer ones

Hey guys.
Today I was reading something about the Valiant.
I saw, that for exampe the 225 engine till 1971 has 145 hp an 215 lb-ft
And from 1972 it has "only" 110 hp and about 170 lb-ft.

Now I am asking you:
Was this just for the insurances or is it really like that?
Did someone feel the difference?

I want to swap from 170 to 225, but there are only newer engines to buy here in Europe