Congratulations on having a near complete set! I know what you mean about open rocker engines being expensive. Back in 2004 when I decided to get back into the hobby I had a NIB single digit serial number open rocker OS .60 4 cycle. I sold the engine to a collector and bought a Futaba 6EXA, SIG LT-40 kit, Super Tigre .40, and the all in one field box kit from Great Planes. I had gotten out of the hobby back in 1981 after getting married and having our first child. The engine was the only thing I kept from my early R/C days.