I will offer a few observations based on the illustrations you provide.
In Figure 1 there should be a hull stencil number visible on the inboard face of the transom in the center, but none is seen. Perhaps the hull stencil number was painted over. If the boat is a 1971, the hull may not have a federal hull identification number. Those were not required until 1972. For more advice about identification of the year of production, consult the FREQUENTLY ASKED QUESTIONS article at
Q1: How old is my Boston Whaler boat?https://continuouswave.com/whaler/reference/FAQ/#Q1The hull as seen in Figure 3 is clearly the older 16-foot hull, without the smirk, definitely pre c.1976.
The console as seen in Figure 2 is very unusual. I doubt it was an OEM product from Boston Whaler.
Figure 4 shows a set-back bracket with power lift adjustment. Some boaters are fascinated with adjusting engine mounting height while underway and employ such devices.
For more help in understanding the historical evolution of the 16/17 foot hull, I recommend you to the REFERENCE section at
https://continuouswave.com/whaler/reference/16-17/Miquel wrote:The seller indicates the boat is 1971 Montauk...
Boston Whaler did not offer a model called the MONTAUK in 1971. Many people unfamiliar with Boston Whaler boats use the term "Montauk" to describe any center console boat ever made by Boston Whaler, and sometimes "Montauk" is used by some to mean any 16 to 17 foot Boston Whaler boat.