There is no 180 HP mod for the TC. One of the problems is there is no type certificated 180 in the appropriate configuration for the TC and no prop to go on it. It would be a spectacular conversion as ther would be minimal weight change and the original configuration cowls would fit.
In a past life I spent time flying a Beech travelair which had normally aspirated FI lyc 180s. Would they not work? Of all the beech products I liked that plane the most.
Twin Comancheeengines have a different angle dynafocal mount to keep them more rigid in the tight nacelle. Travel Air engines also have the carburetor or injector below the engine. They just won't fit. It would be technically possible to create the right configuration to fit the TC but it would be exceedingly difficult and expensive to certify the engine let alone installation in the airplane.
The Miller STC used the IO360 200hp engines and had greatly improved SEL ceilings....exceeding the Turbo'd IO320 numbers without the turbo liabilities. There were some increases in TAS but with increased fuel flows except the IO360 looked good in the mid-teens.