Probably not too far. Early guns fired projectiles at near supersonic speeds but with no rifling in the barrel, the projectile just tumbled and air resistance brought the thing down to earth in short measure. It wasn't until rifling was introduced that distances increased. Having said that, even if it only flew 500m I'm sure you'll struggle to find it.
I'm slightly surprised that the engine stayed mounted. The out-of-balance forces will have been high and the (few) designs I've seen don't look to have a superabundance of lateral strength.