Its definitely not an Air Camper. I have a set of blueprints for the Pietenpol Air Camper and the wingtips are all squared off, pluss its a two place tandem. The aircraft pictured has a single place cockpit. The cowling is reminiscent of one you'd find on a production line aircraft, not the simpler design normally found on a home-built of the era that plane appears to belong in.

Yes, you can measure the engine mounting screw spacing and get a rough idea of what engine size was intended. The bolt spacings of typical .40 class or .60 class engine have remained within a small range for a long time. This of course assumes it has beam mounts and used a glow engine. If it used a gasoline engine, or had a backplate type mounting, it might be harder. If it had a set of bolted on beam mounts and they've been removed... all bets on bolt spacing giving a clue are off.

The combination of bolt spacing and an approximation of the engine's weight would be a very big help.