neil wrote:

Can I ask why you want to remove that nut? Is there something that needs to be replaced? That nut is only there to connect the bevel gear and the shaft. The bearings can be removed without removing that nut. I replaced both of mine by slicing them with the gas axe. One could also possibly weld a fixture to the inner race to pull it off although that might tend to tighten the race on the shaft

The only reason is that it is the factory correct proceedure for removing the inner bearing races, as detailed on the following pages of the service manual. The RHS bearing race is hard up against the bevel gear hub and can't really be pulled from the shaft without having the hub removed from the shaft. However, If I can't back the nut off I might need to look at alternative ways of removing the inner bearing races.
     

a dremel with a abrsive disc will also cut it and easier to control. of course this will destroy the bearing you may not need to cut it all the way through a relief cut opposite each other and a hammer and cold chisel will break it as they are hard steel and thus brittle.
with the cage gone you might be able to get a bearing knife(seperator) behind that bearing it possible its on the shaft so neat that it wont let the nut move.

if i understand the book you start pulling and undo the nut as you pull.

I agree with Neil's advice, at this point I would try splitting the inner race and it'll slide right off. First cut the roller cage so that you can open it up and pull enough rollers out to allow you to disengage the cage and remaining rollers from the inner race - then pack the surrounding area with rags to keep all grinding grit from entering the oil compartment and/or sticking to everything that has oil on it and (without cutting so deep that you nick the shaft) take a thin cutoff wheel on a die grinder or other small device and slit the race most of the way through on a diagonal line.  When you're deep enough, you can take a chisel and drive the tapered point into the slit, which will cause the race to crack, completely loosening its fit on the shaft.  Use all of the appropriate protection when striking the hardened race, as they often shed small razor sharp bits off when they're struck like that.  Here's a video of the race splitting process in action, did this countless times myself over the years - 


 

Thanks Toby, Neil and every one else for your replies. Much appreciate your help. Have a Merry Christmas and I'll report back here with my progress as soon as I can.

Success finally! Firstly I unlocked and unbolted the bevel gear from the hub and in doing so was able to move the shaft hard left and therefore try a pluller on the LHS bearing, the bearing was still too tight and the cage gave way:
   
I then packed rags carefully around the race and using a dremel cut-off wheel on my dire grinder was able cut slits in the inner races as described in Tobys post above. What a job! Those old Timkens are very tough, I basically had to go right through the races before they would crack with the cold chisel, and this took ages becuse I didn't want to nick the shaft and there were two sides to do!:
 
I'm not regretting my decision to replace the bearings!
 
and by 10.30 tonight I had the bevel gear bolted back to the hub, the 1/2" UNF nuts torqued to 85ftlb and re-locked.
 

yes they were knackered. once corrosion starts it keeps going.

I extracted the steering clutch pivot pins and 'cranks' this morning and I'm really pleased to see everything is in exceptional condition.    
however the RHS does have a broken 5B2121 buffer spring which I'll need to find.