Replacement of coach wheels.

Unless your changing gauge,and with a 'handle' of Double00,I assume you not,-I would have thought that Hornby's current Chinese wheels,R8096[I think that's the right no.-it's the plain disc ones you need],would have been perfect for you,-they are virtually identical to Jackson/Romfords but half the price!.
Many people,-myself included, slide them further out on their axles and use them for EM gauge.
You don't say which version of Mk2/3 coaches you have,if they are the old Margate built ones with the plastic axles [especially the square axle type] then I would definately swap them over...
There is no denying the quality of the Ultrascale product,but the price and the waiting time have to be factored in to a project,-they are probably 'over the top' for standard '00' use,-a bit like using 'Rolls-Royce' parts to upgrade a Nissan Micra...

Yes DS239 you are absolutely correct in that my Mk4 Intercity coaches were manufactured in Margate and indeed have plastic inners and square axles.
These coaches were bought in excellent second hand condition, but front bogies are prone to jitters when traversing over points and rail joiners. Replacing the bogies and fitting Allan Gibson wheels has not cured the problem completely.
It is most appreciated in information you provided, relating to the Hornby coach wheels and I have taken note.