Duck- GREAT WORK! But who is the manufacturer?

I think the rounded, smallish windscreen is the clue and I wondered about that. The PT40MKII picture seems also seems to have a longish- "turtle deck" which doesn't match my picture, but perhaps the older version MkI doesn't. My picture has a flat one piece back behind the wing all the way to the tail feathers.

This is only important to me because if I decide to do any mods at all, I'd like to track down the plans and the balance points.

As another question, once you have done modifications to a plane, what's the general rule about a balance point? The thickest part of the wing, and then trim it out and see how it flies? I may post this as another newbie topic, since it applies to another of my old trainers I'm restoring and updating.