es2 home on a flatbed lorry

Whats the history of the bike? when was it last in bits, the engine that is? Could be that the oil pump seal is missing or hasn't been fitted properly. To travel 50 or so miles before it started spewing oil sounds like the crankcase has slowly filled with oil somehow. Either way its an engine strip to some degree to find out. Has the bike been fitted with an aftermarket oil filter? It could be the the scavenge side of the oil system is blocked so filling the crankcase.  A while ago I dealt with a1956 ES2 that had done the same, oil coming from what seemed like everywhere, one of the main leaks was from the timing cover, someone had fitted a new oil pump without checking the compression on the fibre pump outlet seal. The timing cover was sat proud on the oil pump and not compressing the timing case gasket, hence a big leak.   

I have nothing complimentary to say about the RAC, I am a member, but not for much longer. I think if it was me I’d put some oil in the tank and start it up briefly to see if any oil is returning. And look at the mag chain breather and see if any oil is coming out of there - that’ll give an indication of the problem, I think I recall using an o ring instead of the fibre oil pump washer. Also look for kinked or blocked pipes? I assume this is a new problem, ie that it was working ok previously?

... Britannia for many years (but never had to have a Norton recovered!) I'm currently having trouble with a little Yamaha 250 and have needed recovery 3 times. Maximum wait was 1 hour, minimum 30 minutes. They use specialised bike transporters who arrive in properly kitted out vans.

I have bike cover included with my insurance but have never tried it....

Are you sure the oil pump is at fault- is it returning oil to the tank?

... in the timing cover but that's after the feed side of the pump and if it failed then oil would bypass the mains / big end and end up in the crankcase anyway so should be returned to the tank by the pump.

I was with the RAC Full recovery any vehicle anywhere in europe. , I broke down a few miles south of Croydon. I was then 75 years old. I was in a vulnerable state and place . I told them clearly what was needed and they sent a couple of people in small vans to look at me.I was repeatedly told a couple of Hours . No drink ,no food no toilet facilities .After 7 or 8 hours (11pm) i got a relative to bring a van .The RAC do not possess a suitable vehicle .they would have contracted it out except they had no one to do it. I was told they were not busy!. The AA have kit that will carry bikes , RAC do not. Do not waste your money . 

E F Franks (the designer) writes 5/8".  And he was a far greater Norton expert than your pal.

(Of course it's easy to start and tickover at 3/8".  But it will be slower and run hotter.)

If you are running standard compression (about 7:1) you need 5/8", I used to run mine at just over 8:1 and it ran best at about 1/2" btdc.
John
 

...at 5/8" and an 8.5:1 CR. The beauty of manual advance is that you can set it a little bit overadvanced and back it off a bit if it's getting agitated. Then of course readjust it to your new setting.