Mmmm....I'm quite tempted by this. My Mk3 is size 525 and I've always disliked the stack of spacers I have on the steerer to get the bars level with the saddle - I'm 5'6" and the distance from the top of the seat tube to the bottom of the saddle rails is just over 7" (180mm). I could swap all the bits over and then flog my 525 frame for about the same price with luck.
It's interesting that the seller mentions surface rust on the steerer. I found the same problem - the metal was completely untreated, no kind of coating or paint at all, so that the first wet ride the rust was running down the forks from the bottom of the headset. I've treated it and smothered it in Waxoyl which is keeping it under control but I don't know what Thorn were thinking of
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I'll need to have a think.