Here is how I did it.
Several years ago when I rebuilt the 12bolt in the 70 conv, I used a die grinder and a fine sanding disc to make a flat, smooth surface on the bottom of the housing. Then drilled and tapped a hole and used a magnetic drain plug (23011420, still available) for a Chevy oil pan. Too easy! :thumbsup:

http://i65.photobucket.com/albums/h219/DZAUTO/Driveline/100_1476.jpg

http://i65.photobucket.com/albums/h219/DZAUTO/Driveline/100_1477.jpg

Thanks Tom.
Great Idea!!!!!!!!!!!!!!