I read all 22 pages and love when something new pops up in the hobby! Also like seeing young people involved with Mopar's.
My thoughts (I acknowledge no one ask for them
I am in the camp that the car is real and batch special ordered by Mr. Norm. The broadcast sheet special order code and "Street Wedge" does it for me.
I highly doubt the engines were installed at the dealership. It would have been cost prohibitive. I would guess by the time a complete drivable car was purchased, a new engine bought and installed, the 50 cars with the 426 street wedge would have cost as much, probably more, than a street Hemi. It is my opinion the street wedge was installed at the factory. It would also explain Galen's statement that 50 were made. It aligns with another well know special order, the 68 Bengal Charger. It stands to reason it would take a certain number of special orders to make it a worth while endeavor for the factory.
Have you tried researching newspapers from that time frame? Assuming they were batch special orders, my strong feeling is Mr. Norm would have aggressively advertised them and the most popular media back then was newspapers. He was a master at marketing and the best way to move them would have been newspaper advertising. If you find advertisements, they will go a long way in verify the history.
Awesome find, great car, good luck!