The information you got from Chrysler is incorrect.

In addition...

'63 B-body housing: 53 1/4" with 44" perch on center
'64 B-body housing: 55 5/8"" with 44" perch on center (except max wedge)
'71-'73 B-body wagon housing: 59 7/16" with 47.3" perch on center