Well, the gun has been re-finished. The Model 28 had the frame flats brush finished and the dnges beaded. This gun is all beaded. The rear sight has been replaced, but it looks to me that is grooved, not checkered. That means the sight came from almost any N-Frame target sighted gun except either a Model 27 or Model 28. The gun could have come from the factory with the target hammer and trigger, but it is not likely. Chances they were added at the same time the gun was re-finished. Since the font sight is an integral part of the barrel forging, not pinned in, means the red insert is almost certainly an after-market addition by modifying the original sight.
It is still a nice shooter quality Model 28. Why don't you ask the neighbor about the modifications? He may know everything about its history, or maybe not.