Thanks for using Just Answer. I would be glad to assist you.
In 83 the xj-6 came with a borg warner transmission.
In 87 the xj-s (V12) came with both a borg warner and a GM400 transmission.
The borg warner units are different so you will not be able to exchange the transmissions between vehicles.
Please let me know if there is anything else I can do to assist you.
Assistant Service Manager
Tires Plus