N 5166 is 1924. According to the 1924 Evinrude catalog: the tank should be brass the same as a 1923, the carb should be a Zenith with float feed, when the motor is running and you lift the tiller arm the lower unit should swing around and go into reverse mode, lifting the tiller arm only halfway should lock the tilting ability for starting purposes, the gearcase has 3 ball bearings and a stainless steel prop shaft, there should be a drain valve at the bottom of the cylinder water lines where they enter the tower assy.
Your 2 tilt adjusting arms have been cut off. The original tiller and its mechanism is missing. The brass tank and ID tag is missing. This motor is a good candidate for fixing and running as-is. It has character.

These pics show a 1924 N which has an aluminum tank and the sn tag is on the reverse housing. The carb should have an air shutter on its entrance. The tiller arm should have a short rubber grip on it. There were 4 carbs used on the N: A Zenith in ’23-’24 like in the illustration I recently posted, a different carb in ’25 like the carb with the big elbow on your motor, a different carb in ’26 that had a throttle lever cast onto a disc on the starboard side, and a typical Tillotson style in ’27-’28.
Your motor might have a later ’25-’28 muffler but I’m not sure. I think the ’24 N had the same muffler as the ’23 which was a tin can style like Model A Johnsons.
There are a lot of unknowns with the Model N differences between ’23-’28.
There were 6 different reverse housings.