Thank everyone for exceedingly useful replies. The whole microlight world is new to me - I'm stricly spam-can with a little military thrown in for good measure - so there are a whole world of types out there I've never even heard of, let alone seen (though the Thruster is a familiar sight).
So just to be clear, if we can find a type-approved microlight in poor nick, we can do it up as much as we like and it will still be OK for training for NPPL(M)? Who would inspect/sign off the work - is that a BMAA job? (I need to spend some time on the BMAA website, it seems, particularly to find out how I get an NPPL(M) starting from a JAR PPL(A)...)
And no, definitely NOT the Banbury Road - they have girls there these days, you know...! Rather further south than that.
Probably won't make much progress until the school holidays - the exam season was giving me enough time to start thinking about it again but not actually to do much about it yet. But an excuse to fly in to Old Sarum is always welcome...
Tim