Well seller has repsonsed asking for a few more details - at least they are quick at responding. Sent them this:
Thanks for getting back to me so quickly. It looks the same apart from the drain plug nut is small and the one on the listing is bigger, but it's in the right place.
The car is an MGTF 2003 115. All MGF's and TFs share the same radiator layout though so any F/TF radiator should fit any of them. I am a moderator on the T-Bar MGF/TF forum so I could get a couple of the guys to measure as well, but my TF is not modified in any way so they will come back with the same results.
One of them did mention that they had a rad with mountings in the wrong place before on a third party alloy rad they had purchased - so wonder if there are erroneous specifications floating round the net that someone has followed when putting the mountings on this one? There's no massive rush to get it swapped as it won't be going on until I get some stainless underfloor pipes, but obviously if all your rads for the F/TF have been made up like this you may get more issues when people come to fit them after Christmas if they got them as presents.
If you look here: http://www.aaronradiator.co.uk/products/Radiator_Rover_MGTF_02_1_8i_2AU206-1993-1452.html You can see the radiator in question.
The radiator in that picture is in fact UPSIDE DOWN (Even Rimmer Brothers have their picture upside down! You can tell by the drain plug which on the F/TF is at the TOP - god knows why!) but if you imagine it the right way up the top mountings should be 46.5 and bottom 44.5. On your radiator the mountings are 44.5 on both top and bottom.
On this picture from Mike Satur ( http://www.mikesatur.com/images/alirad.jpg ) you can see the spacing on the top mounts is more than the spacing on the bottom mounts
Let's see their response as I imagine he's concerned now as he probably sold a few for Christmas pressies that haven't been even opened and tried yet!