mbat, I know what you are attempting to do. It is a little different than what I did since the MC was already mounted high and I could use the same hanger mechanism. I have heard of people changing to an upper mounted dual MC in the older cars. You might get some responses from people who have actually done this over at the Jalopyjournal.com website, then navigate to the H.A.M.B. sub forum. Lots of older cars there and it is free to join.
http://www.jalopyjournal.com/forum/