Triumph Repair: gt6 add j type od?, output shaft, input shaft

Question
Hello,
I picked up a 73 gt6 mk3 with a four speed.  Bought a used j type overdrive.  Hoping I can make it work.  I do have the tranny that the OD was attached too, though it doesn't seem complete enough to rebuild.  The OD seems as though it would mount up to my tranny, albeit there is an extra hole on the top left of the OD case.  Any potential here?

Answer
Hi Jacob,
I have made this swap on other BLM cars but have not done it on a GT-6. However, I believe it is the same.
You will have to disassemble both boxes to confirm that it will work. The mainshaft (output shaft) needs to be changed. So you need to remove both mainshafts and compare them. All of the splines forward of the back of the trans. must be exactly the same and note the forward end of the shaft to confirm that the bearings will work that go between the input shaft (1st motion shaft) and the mainshaft. Then compare the bolt pattern of the OD adapter plate so it will bolt up OK.
Also you will have to wire up the OD so as to NOT allow the OD to engage when in reverse. Look on your shift tower for extra switch positions for safety switches. If you don't have them you will need to wire in a safety switch and warning light so you only engage the OD in 3rd & 4th gear. I had one wired up to just give a large red warning light connected into a back-up light switch to remind me to be sure the OD switch was OFF. Another method would be to wire in a relay on your backup light circuit to iterupt the power going to the OD solenoid.
I had a A-H 3000 come to me in a shop with the OD exploded. The owner thought it was cool to have OD in all 4 gears but forgot and left it in OD when he backed up.
I don't know of any extra holes in the trans case when ODs were installed.
Let me know how it goes,
Howard