Well, I got a chance to talk to Richard at Keisler again and he told me that yes you do have to cut the rear crossmember on the a-bodies. The directions are not very clear on this at all. IMHO. He did inform me that the Keisler tranny mount was over engineered in order to stregthen the cutout rear crossmember. He is a super guy to talk to and is very helpful. This was helpful information that I wish I would have known beforehand. I may not have been so upset about cutting the rear torsion bar crossmember.
Anyways, my drive shaft should be arriving tomorrow so I may pull the old rear and get things started on the rear this weekend.
Word of warning>>>>>you do have to cut significantly for this project but it can be done. Good thing I have lots of patience.