In the early production year for the 1963 426 Max Wedge cars were referred to as Stage I.
In May 1963 until late June, Chrysler produced what is referred to Stage II 426 Max Wedge cars and in 1964 Chrysler produced what is referred to as the 426 Max Wedge Stage III cars.
I hope that helps to understand what all the Stage stuff is about.
I have a late June production model 1963 Plymouth Savoy 426 Stage II and a 1964 Plymouth Belvedere 426 Stage III.
So the error in his listing is that the car could not be a Stage III Max Wedge.
I have a suggestion for you, get a look at the fender tag and see when the car was produced, early 1963 or after May 1963. And if it is a real 426 Max Wedge, the fender tag will tell you that too.
All the best...MadMax3426