I have recently looked into using a Weber 55 DCOE side draft carb.
Pretty cheap at about $560. I was surprised. Not easy to lean the mixture as it is a
very complicated carb. It will work but the idle will be pretty poor
as it must be mounted on the beginning of the p-port intake runners.
The throat spacing is too close to mount it near the P-port rotor housings.
Besides that it would be subjected to the full heat of the exhaust manifold. Power will
be somewhat down compared to a slide throttle due to the aerodynamic
drag of the butterflies and throttle shafts. I don't know how much. If you take out
the throttle shaft and butterflies and use a slide throttle you will
lose a lot of functionality like the accelerator pump for one example.

It should work fine unmodified at low altitudes and with a modest HP penalty.

Ken Welter has been flying a Weber for a few years on his Coot. I think he
is tricking the float chamber by using dynamic air pressure to lower the fuel level.
I am not sure. I don't fully understand what he is doing. Perhaps that is
possible with a needle valve.

Paul Lamar ...No rotor no motor.

  If you look at that photo just above the left velocity stack is a
hole that is a float bole vent, I have a controllable air ram pointed
at the velocity stacks that will increase the pressure on the Venturi
so it will draw less fuel the rams are about an inch away from the
velocity stacks, you can also use an air bleed system that pulls on
the float bole vent and it will also lean it out which they do on
snowmobiles.
 Also the Weber carb very sensitive compared most carbs and when the
air is thin it draws less fuel so it compensates to some degree but
needs some additional manual leaning.
 Ken

No pictures came Ken.

Paul Lamar