Thanks team, appreciate the responses and confirmation. Fortunately I purchased new Timken replacements and all of the necessary CR seals (thanks Toby for your detailed sizing and crossover info) months ago in anticipation. I'm thankful I did now!
 

I managed to dismantle the RHS clutch assy today. Pleased to see the condition of the metal discs are good and will be able to be used with the new Bimetallic frictions.
 

neil wrote:

How many hours is it estimated that this tractor has done?

Have a look at the title of the thread Neil 
However it now shows 3960Hrs - I'd haven't kept it idle!. Looking at everything I'm certain these hours are orginal. They have no reason not to be, as I brought it from the grandson of the orginal owner and It had been on the same farm all it's life and was always shed stored.

neil wrote:

Ah apologies Mark, this thread has been around so long I didn't bother to look at the title - thanks for pointing that out : ). Do you happen to know if the clutches have ever been done on it? They're pristine. I'm sure shed storage and not running it in wet conditions too much have contributed to its longevity. It really is in great shape
 

Thanks Neil, I don't know for certain but as far as I am aware these clutches have never been replaced. The only major works (according to the original owner) was that the cylinder liners and pistons were replaced at some stage as the engine got dusted. I did find the cylinder numbers etched by hand into to connecting rods and caps (see below) which would indicate that the engine has been in bits:
 

Well, the next thing is try and move the 3" nut between the bevel gear hub and the LHS bearing. I made this fixture, which was modeled off Tobys design, which holds the RHS hub in place on the splines, but so far haven't been able to shift the nut. The only tool I have that will fit across the 3" flats on the nut is this large pipe wrench (not ideal I know) and that coupled with a meter long cheater hasn't managed to shift it! Any tips anyone?
     

I'm stuck chaps, this is the only thing on the tractor that has stumped me so far. I managed to bend the handle on my 24" pipe wrench and still the nut won't move, even with another 400mm on the end of the 1meter long pipe! Any ideas? Anyone else struggled with this? Can I unbolt the bevel gear from its hub and shift the whole bevel gear shaft across to the left far enough to pull the LHS side bearing from the shaft and off the back of the nut? 
 

i assume it the red nut your trying to undo. straighten that lock out a bit more.
if you have a gas axe id cut a spanner out of a bit of 1/2 or 38 plate atleast if you bend it its only a bit of steel and not expensive tools.

are you turning it the right way? is it left hand thread or something sometime doing it up first can get em to release as the thread has pulled under load and the slight tightening straitens em enough it will then undo be careful though as thing can break doing that.

It's this nut, circled in red. Sandwiched between the bevel gear hub (colored red) and the LHS bearing:
 
Toby has a detailed episode on how to loosen this nut, remove the bearings and pop the taper on the bevel gear hub which I have copied below. I've tried to follow this to a tee, only that I can't shift the nut: