I am currently building the Valueplanes SE5A 1/4 scale WW1 biplane. This plane can be built electric or gas powered. I am going gas and was considering the NGHGT35R. This engine puts out 4.22hp, has a rear mounted muffler and is in my budget range. This plane when finished will weigh about 18-19lbs. Would this be a good engine type and fit for this size plane? I would consider other engine makes but cost is what is the deciding choice of engine. The cost of this kit was decent compared to the Balsa US kit. Any help in this would be greatly appreciated.

For models of the SE5a, Fokker D7, Spad XIII and the like 35CC engines are kind of the baseline. You can go as light as a 25CC class engine on planes planes like a Camel, Pup or Triplane but models of the larger liquid cooled fighters usually need the additional horsepower. I've seen planes with lots of detailing that flew on 50CC class engines. Given that I don't know anything about your building or flying habits I would recommend being conservative and shoot for a 40 CC engine.

Large, dragy airplane with a light wing loading, 3-4 hp is all the useful power needed.

CG requirements though demand 4-5 pounds in the nose of this plane ( WW1 design ). Lead or bigger motor then is the real question.
The NGH 35 will power this plane very well with no problems. Just add lead then to balance, nothing wrong with that.
IMHO