There was also Tartan fuel made for the Tartan series of engines which only needed about 7% oil as a glow . The diesel was also a low oil mix. The Tartan single was really a winner on that fuel and flew 90 inch models with an 18-6/7 effortlessly great performance for only a 1.4 C.I. conservatively ported reed valve engine.
One of our steady contributors has a Tartan Twin with 2 heads and a ST60 carb. 25/7-8 inch props are not out of the question as it would probably match a 4.2 C.I. in output.
Dennis