1953 chev panel

[BSG]

anybody know where i can get a retrofit overdrive for a torque tube rear end?
in tom brownell's HOW TO RESTORE YOUR OLD PICKUP he list an outfit called overdrive inc in portage oh ( bob green and willis berkstein?) who were retrofitting borgwarner od's onto the front of the differential and shortening the tube. they seem to have disappeared. i also saw a picture of threakill????( made in oregon) unit mounted mid shaft which i haven't tracked down yet. i figure if it was done once and worked well it can be done again but i don't have the skills or equipment to do it myself. thanx tom