B Body rear into 67 cuda fastback

It's my understanding you can bolt in a '66-'67 B-body rear without moving the perches as they are narrower than the '68 and newer ones. Seems like the perches are about an inch further apart total but you can pull the springs out by hand the half inch or so on each side and just bolt them up.
Some will argue this is bad but others have done this on cars they drove and raced without any ill effects.
Just a thought,
Dallas