A body 8 3/4 or B body 8 3/4 ?
One more time...a 66/67 B body 8 3/4 is a DROP IN for an A body.
No cutting, welding or drilling required.
The 68-70 housing is wider. The popular chart showing all 64-70 housings as the same is INCORRECT.
If you have a "29" body (Duster, Demon, 67-69 Barracuda, Sport), it will look BETTER than the factory.
If you have a "23" body (or 1st gen Barracuda), you will lose about 3/4 inch outside wheelwell clearance per side.
The disk brakes are what makes the front track wider on Dusters.
The 66/67 Axles puts the rears on nearly the same track as the disk front.
Your "29" body Cuda will be fine, shouldn't rub, and look great.
...and it's 3/4" per side at the perches. You can simply push, and it drops in.
I ran mine for years.
This has got to be the second best kept secret in the Mopar world!
This is what it looks like-