Hi,
Peugoet built motors like this from 1904 - the three-bolt mount at the back is a give-away. This is probably the 2 3/4 h.p. model (about 350cc) and was their first motor with a mechanically-actuated inlet valve. I'd expect to see PF cast in the crank case under the timing chest, but either Peugeot left it off this model, or the motor was built for use by another manufacturer. You'll need to find a Peugeot expert to get the fine detail.
Leon