Terry,
Many of the Supercar dealers did in fact sell some of these cars. Motion did many SS427 Impalas and Biscaynes. I do not know of any converts that were modified by them other then them being sold through the dealer. Most of the cars I have seen or heard about were RPO cars and were sold as delivered since everything was already in place sans headers and traction devices. We barge people get little respect due to our size and nameplate so don't take it too personal.
Try loggin in over at
www.impalass427 as well. Ask for Mark as he is the lead guru on the SS427 though I am not sure he has much information on cars such as Baldwin Motion.
Rick