For the 1/5th scale Zero (recommended 50cc-60cc engine), I think the 77cc Evolution would be a good fit IF it fits under the cowl. This engine is 9.1 inches wide so if your cowl is more than that...you should be good. If you compare the specs from this engine and a DA-50...they're pretty close except for weight....the radial weighs almost twice as much.....but this may be of no consequence....if you need to add weight to the front anyway....which I would think you would need to do. This airplane was probably designed with a Zenoah G-62 in mind....which is comparable in weight to the Evolution.
DA-50: 2.7 Lbs (without muffler) 5+ HP
Evolution 77cc Glow Radial: 5.7 Lb, 4.7HP
Zenoah G-62: 5.1 Lb, ~ 5HP

If performance is the goal....definitely consider a modern GAS 2 stroke engine such as the DA-60, DLE 55, Etc. If scale is what you desire and you have the means to afford the radial....go for it!

CB