I am being a bit lazy with my research here but maybe the very recent information I received will update things.
This month I placed and order for a 304mm 2 piston front upgrade kit for my 2004 TF from Rimmers. They accepted my order but sent a note to say that they had shipped it minus one of the callipers was no longer available. So how they thought that this would be of any use I do not know! My question is whether there are any sources of this kit or at least the component parts? I notice now that Rimmers are now saying in their catalogue that the kit is no longer available.
I live in Spain and the original order actually was returned to Rimmers as it was banned restricted material! All part of the joys in buying UK things after Brexit.