TRY H&H IGNITION SOLUTIONS ,UNIT E FENS POOL AVE , BRIERLY HILL , WEST MIDLANDS, DY5 1QA TEL 01384261500 They can do your mag it will come back like brand new , have used them for mags from old boat engines dynostarts and all sorts never had any problems with them and very helpfull too !
There is a fella in Surbiton South London, Jay Electrics who could probably do it, very cleaver old school rebuilds, alternators and starter motors worth a try 02083911004
Petrol is for washing parts, Alcohol is for drinking, Nitro is for racing!!!
Thanks Jim and John, will get on the case - I dealt with H&H a few years ago for a magazine project car and they really seemed to know their stuff, but if I can take it somewhere more local that will be handy so I'll try Jay first