Chris,

that is a Dirty Birdy 40 and the correct engine for it would be a side exhaust 45-46.

The cowl looks like it is simply cut for an upright engine installation (hard to tell from the sole angle). DB40's were not designed to use a pipe over the fuse top. Instead, a proper canopy should be fitted and it can be obtained from Keith at Park Flyer Plastics. If you want to pipe the engine which is certainly appropriate, you should use a pipe on the side of the fuse.

You make reference to a "plan" but I assume you are talking about the model. If you have the actual build/design plans, it will tell you all you need to know. I'll look up the CG distance and post it later.

I hope this helps.

David