The only part of the GT6 that I left relatively untouched was the engine ,gearbox and overdrive. The reason for this was I had the car Started and moving around a small yard before all the rebuild work took place. Alas after only a few miles of driving, the clutch thrust bearing started to make noises that resembled a small cage of birds.
since the car has been put away for the up-coming winter months I thought it would be a good time to undertake the necessary work.

There are a few ways this can be done. The first is to remove the engine and Gearbox as one unit. Then remove the GT6 gearbox from the 2 litre Straight six engine. Change the clutch and rebuilt in reverse sequence. I decided to go the other route and remove the gearbox from within the GT6 cabin, while leaving the engine in place.

Here is a list of Parts, tools and instructions on how to achieve this.

Parts
Clutch plate,
Clutch cover,
Thrust bearing,
If worn, Bearing carrier and actuation arm. Check for wear at the point that the arm engages the carrier ring
Gearbox Oil, ( EP90 for topping up. EP75w-80 or EP75w-90 for filling from empty.)

List of tools
Ideally 2 people
Trolley Jack,
Axel stands,
1/2″ Spanners,
7/16″ Spanners,
9/16″ Spanners,
Socket set to fit above sized
clutch alignment tool

Removal instructions

Disconnect battery (Important)
Remove passenger side glove box.
Remove gearbox tunnel carpet.
Remove gearbox tunnel
Passenger seat removal is optional. be careful not to scrape or damage it if left in.

Disconnect propshaft. (4 x 9/16″ bolts, nuts) this may require rocking the GT6 forwards and backwards to gain access to all bolts from the cabin area.
Disconnect speedometer drive cable.
Disconnect reverse switch and overdrive unit wiring (If fitted) see picture below.
Remove the Clutch slave cylinder and actuation pin, that is located in the cabin on the bell housing by releasing the 2 1/2″ bolts

Jack up the front of the GT6, and rest securely on axle stands
Chock the rear wheels to prevent the car from rolling. (Important)
remove the jack, and place under the rear of engine with a substantial block to support the engine weight.
Raise the jack to take the weight of engine and gearbox. (not lift, just support)
Remove the engine starter motor, 2 x 9/16″ bolts
Remove the gearbox / chassis mounts in the cabin, they are located on the underside of the box, and to the rear. 2 x 1/2″ bolts
Now begin removing bell housing bolts. Start from the bottom, as this will leave the top 3 studs still supporting the weight of the gearbox. 1/2″ nuts and bolts. Note: two people make this job a lot easier. 1 on the engine side with a 1/2″ spanner and 1 on the cabin side with 1/2″ ratchet driver. (See pic)

Once all but the top 3 nuts, on studs have been removed, remove the 2 nuts either side of the central stud/nut. clear the engine earth strap out of the way.
Now slowly undo the top nut on the stud. As it is undone you might find the gear box slowly start to pull away from the engine plate. Just support the rear of the gearbox.
Once the nut if fully off, I would recommend one person in each foot well. hold the rear of the gearbox, pull and wiggle slightly until the gearbox bell housing has pulled away from the engine block.

We found it easiest to lift the prop shaft end of the gearbox, and rotate it into the passenger side foot well. Some jiggling was required to clear the bell housing front under the lower dash rails.

Once the gearbox is clear you will be faced with 6 1/2″ bolts around the edge of the pressure plate. gradually undo these in a criss cross pattern to prevent distortion on any mating surfaces.

Now take your new clutch plate and alignment toot and offer it up to the flywheel. Make sure the plate is the correct way round. “flywheel side” is written on the side that mates with the flywheel.
Now offer up the new clutch cover. this should locate on the 3 dowel pins next to 3 of the 6 securing bolts.

screw in the 6 securing bolts by hand until starting to apply pressure on the cover plate. Then proceed to tighten them gradually in a criss cross manner. Again, this will prevent distortion of the new cover plate. the result should look like this,

While the gearbox is removed, it is always worth replacing the clutch thrust bearing. this sits in the bell housing on a carrier, Just slide the carrier of the main shaft. carefully drift the carrier off the thrust bearing. fit the new bearing to the carrier by drifting of using a vice/press. Note: never drift bearing on the outer race. this will damage the internals and undo the good work you are undertaking

The reassembly procedure is the reverse of removal

Amendment

It must be said, (as pointed out bellow) This is a convenient time to check / replace the gearbox oil. Either when the tunnel has been lifted out, when the gearbox has been removed or just re fitted.
Advisory: Try to ensure when checking the fluid levels that the car/ gearbox are sat as level as possible to ensure the fill plug drains the oil at the right level, weather in car or on the bench.  I would recommend EP90 for topping up. EP75w-80 or EP75w-90 for filling from empty.  The fill/level indicator plug is located on the right ride of the gearbox and is removed using a 1/2″ spanner on its square head.  Fill slowly until you start to get some run-off coming from the fill hole.  Leave the unit to stand for a few minutes thenreplace the square headed plug.

Many thanks to Chris Cook.