I went out to walk the dog and think.
The bush I have fits the small 1.242" journal very well. If we think the journal is big enough to carry the running loads without cracking, I will machine the oil way as an annular groove in the thick wall of the bush, not the journal - this will have the same affect as the original groove in the journal.
I guess when SRM sleeve the journal for the needle roller conversion, the shaft is a bit smaller than stock, for the roller sleeve to fit over it - and as Muskrat says, he has a 1.181" t/s journal - which I guess is performing OK, so maybe mine is not fit for scrap just yet.
I have three alternatives - my home grown approach described above; asking SRM to resleeve the journal at £107, or thirdly got for the full needle conversion at about £550.