Welcome to the forum. Your FJ40 really is beautiful.
Re a experienced 40 series mechanic 'near London' I would recommend Karl at Ducks Cross 4x4. He's based between Bedford and St Neots at Wilden, MK44 2QW. 01234 376609
He is always busy so I suggest that you mention my name when you speak with him. IMO he is the best. I bought my 40 from him 16 years ago and he'd done all the mechanics on it and he does a lot of restorations (obviously not required on your truck).
Over the 40+ years I've bought and sold plenty of vehicles but only one buyer/seller has become a friend and it's Karl.
Regards,
Rodger