Looking at the pics of the Bally Bomber, which is an amazing accomplishment, it looks like the unit between the prop and the engine might be a supercharger of some type.
Which got me thinking, Lycoming has that big flywheel on the front, turns 2700 rpm, replace it with a squirrel cage type fan, would it produce enough usable air to give a few inches of boost?
Relatively easy to build.
I remember reading way back when EAA was doing the mogas certification they had used an electric fan into the intake during ground runs and had seen "significant" increase in power.
I played with a Kcar with turbo many years ago and was impressed with the small amount of air pressure produced by the turbo which made a large difference in hp.
There was a discussion, I don't remember if it was here or on the Rvaitor about the ram air effect and it turned out to be not that big a deal.
I have an RV style carb heat and notice very little difference when I close off the ram air and draw air from under the cowling.
Turbo's are a small fast turning fan and we all know a big slow turning fan moves more air so maybe a 12 inch squirrel cage turning 2700 rpm might move enough air to make a difference?