dress watch

Congratulations, but I'm curious to learn why you are convinced that the dial is original? Have you dated the watch from the movement serial number? Is it a cal. 8521 or 8531?

Well, although I cannot be 100% certain, I do not believe that the dial, nor the lume on the hands are likely to be original to the watch.

I have owned more than a few Ingenieurs over the past 25 years, including black dials, and a ref. 666 was my first "good" watch. I would never expect a 55+ year-old watch to have such bright and well-preserved lume, nor signatures on a black dial. Also, the Ingenieur signature is a later, thicker version. Here is the type of (finer) signature that is typically found on the earlier 666 dials:



The lume plots on the dial are also suspiciously well-preserved, and "T SWISS T" was not typically found on the earlier dials.

I would surmise that the dial and hands are service replacements, but I could be wrong.

What is the condition of the case and movement?

The black one to which you linked on the IWC forum is from 1964, so not a taut comparison.