You need someone, maybe your wife's grandpa, who can spend some time with you on the engines. It doesn't make sense that a glow plug would get cross threaded on the way out. Someone knowledgeable should have a look.
A 5 foot wingspan is normal for a 40 size trainer. Often they are a larger than that. For example, a Sig LT-40 has nearly a 6 foot span but flies well as a trainerA on a mild 40. A 60 size trainer will typically be at least 6 feet. A 150 size trainer...beats me, but it better be a LOT bigger than 5 or 6 feet.