The IBM card shows G Code 383-4 VIN, ENGINE CODE 62 383-4
The Broadcast sheet shows G VIN 383-4, sales code 62 383-4 and engine assembly code 180 383-4.
The Fender tag shows engine code 62.
All three show 699 Special order but not WHY is was special order. It could have been SPECIAL ORDERED for a variety of reasons none of which would be related to the engine.
The factory documents show 383-4 not 426 W. There is an inconclusive reference to a 426w on the BS.
I agree the 426 reference is interesting but there is NO proof or documentation this car came equipped with anything other than a 383.
Wishing, wanting, and hoping are not documentation nor proof of anything. The factory documents show this car was built as a 383-4. Nothing more and nothing less. Not my opinion. Not my belief.
All I've asked for, all I've ever asked for, in this thread is proof and documentation. So far, all the factory documents show is a 383-4.
Again, and for the last time, I truly hope you get to the bottom of what you have, accept any truth and go with it.