Gas/Glow: .Depends.
What support equipment do you have ?
Glow engines are a bit cheaper up front than a typical gas engine.
Gas engines will require an extra battery for the ignition.
Do you want to spend $18.00/gal on glow fuel or do you want to mix gasoline and oil at $6/00/gal?
My 46 glow would get around 11min run time on 8 ounces and my Evolution 10GX gasser gets around 25 minutes on 8 ounces.
For a 20+ year old plane from a barn , I would run the engine it came with until the bearings let go(probably rusted now anyway) and if the plane held together then consider another engine. Again no pictures of what you have so ................