Pleased to report that after a fairly easy fitting process the scope fires up as a B model. It's noted in the 'About' page and the keyboard selftest map has changed to reflect the new front panel. The changes are only moderate but, I hope, helpful.
I will probably keep the old panel as it's a spare LCD and switch/encoder set but I wouldn't rule out selling it someone's really keen.
This scope has been a great purchase. I bought it secondhand a few years ago for, I think, £1200 as a DSO7014A. Even then I was delighted with it. As a result of the thread elsewhere on this board and this new panel it's been upgraded to an MSO7054B (actually, I haven't fully modified the input compensation yet, but I will). I love the big screen, the traditional HP construction quality and the lack of Windows OS. I'm unlikely to change it soon, though the new generation of 14-bit ADCs is exciting.
Thanks for pointing out the panel. I looked around for a broken one a while back but never found one - had pretty much stopped looking and even now didn't spot it back in october (probably wouldn't have paid the price then, either).