RV-4 Power
I concur with the light is good recommendation. My -4 is ~950lb empty with O-360-A1A, Ellison, and wooden Hendrickson prop. I get 170KTAS @36L/hr, not the fastest about but OK. Empty Cof G is at 17%MAC, and when doing aeros I would prefer the CofG to be back further. I strictly can't do aeros with a pax due to the aerobatic gross of 1350lb, with the 200hp engine this limit could be exceeded solo! With 180hp the aircraft is overpowered, and I wouldn't consider putting a 50lb (and $10000) CS prop on it as it would restrict the payload too much. For general utility, the 160hp engine and extra fuel/baggage/pax would be the best combination in hindsight, BUT, if you do find a 180 engine at a good price, buy it, but build light.