TBH you may not ever get a solid answer. There are a lot of airplanes that follow that general planform and it has, as noted, been modified. The interior looks like other short kits of old production kits that I have seen. I'm betting that if you unscrewed the sheeting on the bottom of the fuselage you will find bell cranks going out to the linkages on the tail surfaces. That's not a thing you often find on a production kit. Is there a bell crank out to the ailerons? Or is that just an old servo arm on the linkage?