An available engine is the Evolution .61NX. It is very light for the power it makes. Don't run anything more then 15% nitro unless you add a head shim or two. Even 15% could use an extra head shim. Mine on the recommended header, pipe and an 11x7 APC turns 13,800 to 14,000. I don't believe anything that is as light will turn as high.

As to old engines not available anymore, my favorite was the O.S. .61F-SR ABC with the exhaust port raised. Great power for the time. But I have to agree, the Tigre G.60 ABC was a great motor. Glad a have a new one!