Hi,
I would definitely vote for a 4 cycle twin made by any of the well known manufacturers. My 1/4 scale Proctor Nieuport 28 is powered by an OS 160 four cycle twin. It has a short take off and will loop from level flight. My smaller Proctor Nie 11 is powered by a Saito 100 twin which is an absolute jewel of an engine but is too small for your purposes. One of the advantages that is not often mentioned to these twin engines is low vibration. When you have lots of scale wires, turnbuckles, and scale framework you don't like to see it torn up by a big single or gasser, not to mention the potential problems with increased radio interference from vibration.

There is an experienced Proctor flyer on this forum who is planning on building an Eindekker in the near future. I'm fairly certain he decided on a Laser 200 to power it. His name is PITTSDRIVER and hopefully he'll join in here. If not, you may want to email him for additional info. Best of luck with your project and hope to see some building pictures here soon maybe?