[theOshkoshModeler]

Originally Posted by Jan Kytop

I think that Fiddlersgreen have a B-52 testbed for X15

That was my first assumption as well, but you can see an actual cockpit interior inside the nose very similar to that of GPM's B-52. As far as I can tell based off of photos of FG models, they usually don't put effort into a cockpit interior (partially because they work with such small scales to where an interior would be highly impractical).

Taking a close look at the parts layout, especially at the engines, they're a lot smoother than FG's B-52. FG only uses 3 parts for each engine, but this one looks a lot more like GPM's approach with 7 parts covering both engines.

Also, here's two more photos for everyone else if it helps to narrow down (not to give Alice more credit than they deserve, but these ones include other angles and the attached X-15 underneath the starboard wing).