Sounds like a good deal, one I would be tempted with (although no cash for that at the moment!)
However. at that price I would expect the inner wings to be completely fecked, you won't know till you take the outers off, also check around the windscreen for signs of rot as thats another place they go...
MG B's are fantastic cars, but rot like anything
Also add yourself to the "Classic & Sports Car Modders" Facebook page, tons and tons of knowledgeable folk on there about the MG B's
and Martin's home page
http://www.kewengineering.co.uk/upgrades4mgs/index.htm has tons of tips and tricks about them too