I love this stuff. I really don't have a clue, but here are some observations.
It appears to be a water cooled v8 with shaft drive. Since the engine is mounted longitudinally, it's not the famed Moto Guzzi v8 gp racer, but it does appear to have a mount for a dustbin fairing. You stated that it wasn't built in the 50's, but it has drum brakes, leading link front suspension, twin rear shock suspension, so unless it's a retro replica, it has to be 60's or earlier. Dustbin fairings were outlawed in gp in the late 50's, so I'm at a loss.
The water cooling has me guessing, so I'll guess it's Italian in origin. Even close on date and origin?
This is a good one!