If it has to be 26cc engine then go for Evolution/MVVS 26 with tuned pipe. ZDZ F3A 40RE will give you the extra punch if needed. Also consider glow is weight is an issue. YS 170 will give you that needed reliability and power.

I have MVVS 26 with pipe on Epsilon 160 F3A pattern plane. It's little over weight limit, but getting lighter in this summer Just forgot Zenoah, china engines and sidecarb engines.