318 and 833 swap into 72 sedan

A pickup 833 is going to be long shaft, same as B/E body. You really want an A body 833 which is shorter, has the shifter mount in a "better place" and is same length as a 904. B/E/ pickup/ van 833 is long shaft, same as a 727

The problem is not the shaft length, nor the mount. The problem is the shifter mount. If you search, around the WWW there is a diagram to build an adapter plate to use B/E 833 in an A. I don't think, however, this works under a "stock floor." Could be wrong.