Sorry John,
I think we might have got our wires crossed a little.
I have a mk3, with an ITM carbon fork (fitted from new) and I have the old steel Audax forks (with low loader bosses) which I have never used.
I was trying to decide whether to replace the carbon fork with either the standard (mk 4) or try to find an 853 pair (I rather stupidly didn't realize Thorn had discontinued them and they had sold out in 46mm offset). A friend of mine has offered me a mk3R in my size with standard fork, I might just get that and let my son ride the mk3 in a year or so, as the extra tyre clearance would be very beneficial to me.
As for the 853 bike, I would love one but maybe a slim chance!
Kind regards Matt