RE: Junk plane to test gas engines with
I'm using the Great Planes Escapade .61 for this exact purpose.
I wouldn't call it a junk plane. It's actually a fine model that flies very well, but it's relatively cheap and does not need expensive servos etc.
I like it because it has the open cowl cheeks option and there is a magnetic hatch above the fuel tank which makes access to the ignition modules easy.