Octane isn't power, its ignition at a higher temperature to prevent
preignition in a high compression ratio engine.

You don't say that the engine runs poorly - coughing and sputtering -
only that it lacks (acceleration) power.

A carburetor works on the Bernoulli principle - that rushing air will
draw a liquid into its stream. To that, an acceleration pump is added to
kick extra fuel for acceleration, otherwise the air / fuel ratio would
become too lean as the throttle is opened. The engine will cough and
sputter if the air / fuel mixture is too lean (fuel starvation) which
you don't cite.

These new carbs - do they have similar size venturis as the old ones?

I suggest you first check that they're the correct size for the engine.

Or, if the power reduction is not large, it could be that the old carbs
were set too rich and, though nice to drive, were gross HC polluters
that no longer could pass an emissions test. If that's why they were
replaced then that's the answer to your post.
This engine will run well with the proper air / fuel ratio but do so
without the robust torque that you've become used to.

Are you in the Vancouver BC or northern Washington area? I know a guy who calibrates carburettors, his 1958 220 and 1967 200 run
like new, people swear by this guy. If interested then reply.

cp

No.