OK so the Hiper did have the R2000 DC4/C54 engines which is what I had heard.
Now I never flew in one, knowingly, but heard many takeoff and land and they ment business. One thing I do remember is that the prop-shaft was a bit longer in the R2000 as fitted to the three's than in the standard engine so the propellor stuck out a bit more away from the cowling.