I have installed a KT-74 ADS-B out transponder and have the original transponder from my '83 J-model for sale. It has a yellow tag from 2008, and was fully functional when it was removed in December. The digits rotate smoothly and the white numbers are still sharply contrasting. There are typical small cracks in the plastic on each side, seen in the pictures. It includes the transponder and tray as shown here. No cabling or anything else not seen in these pictures.
$500 including basic shipping within the USA. Paypal preferred. I am in SoCal, if you want to meet for a $100 burger somewhere in the area to make the purchase.
thanks, -dan