I talked to Bendtsens transmissions at Back to The 50's in Minnesota and he quoted me $3,800 to convert my Slim Jim to a 700R4 on my 61 88. This included the tranny, modifing the floor, and everything so it would be a turn key deal. I didn't think this was too bad considering all the work involved.
http://www.transmissionadapters.com/gallery.htm
Pat