I find it hard to believe the Franklin Sport 4 engine is not being produced as a kit of engine parts to be assembled for home built airplane builders or a shop the way it was 50 years ago. No FAA TC is needed. The Franklin Sport 4 could be upgraded to solid state ignition, automotive spark plugs, Bing carb and other external changes similar to the Jabiru 3300 engine selling at an affordable $20,000. The Sport 4 has 235 c.i. (125 hp) but weighs the same as the Continental O-200 about 210 lbs. The small Continental and Lycomings are 1940s production technology. From the responses I've got, some are negative about the Jabiru 3300 engine quality. Yes they had more than their share of problems initially but the Generation 4 version solved them. Kitplanes magazine describes the details.