Sorry to bump this up, but figured the information might be useful at some point
I did end up fitting my threadless YST bottom bracket, however I did it on the cheap... Rather than using 2 splined BB tools, I used 1. It worked absolutely fine and it hasn't come loose or moved yet.
Secondly, I didn't use a proper 45 degree facing tool, but rather a bunch of filing with some small diamond files. Tbh, as long as you file fairly evenly and knock any high points down the bb should sit fine.
All in all, using this cheap fix worked well, so anyone with a knackered BB shell might want to try this before getting new shell threads put in etc...
One note is that the bike is fixed wheel, which possibly makes it a harder test on the BB... still, it works fine so I'm happy
Sorry about the bump again,
For Sale MTB
1948 Holdsworth La Quelda
196? Henry Burton Track Bike
1980 Carlton Corsair Fixie
199? Saracen X-lie
199? Bianchi Grizzly