OK .... the drop-outs looked very very much like Airborne, except for the slight hump for the mudguard / rack. The chain pip is a very odd characteristic of "most" things from that particular factory. There own frames are HiLite and they make for Van Nicholas amongst others, they also use rather thick drop-outs too. The canti-bosses also look similar, but I will need to get back to you on this.
I saw a photograph of a Willits a while ago with similar drop-outs, but I would be surprised if it was. It's probably old with the downtube gear cable stop. I don't think it's a Raleigh either. If it's USA exotic, there's fewer choices. I think Dean did a mono-stay, but I think at this time it would have been produced at the Sandvik / TST plant and would have a signature stamp in the BB.