Pete
Not sure about the head mill, but
Brian can certainly do the valve seats - and most other engineering-type things, too.
He's got a little olde tyme engineering shop in Bexley - swarf and bits of stuff everywhere - but he's pretty reasonable and good fun. He's got plenty of experience with bikes and has done the seats on my 350 and 450 twins. He's also got a box of bits for my 750 to work on - replace the valve guides, recut the seats, fix stripped threads, TIG frame sections, drill out a couple of frozen bolts and some other odds and sods. From the look of the workshop, I'd guess he can probably do the milling too, but even if he can't, he'll know someone reasonably local who can.
The only real drawback I've found with using him is that his turnaround times can be a bit unpredictable. And the one thing I know he definitely can't do is rebores, but I know a guy in Sevenoaks who can (he's pricey, but a little more reliable time-wise).
Incidentally,
Brian's just around the corner (nearly) from the good guys at
Modern Screws - a great place for stainless nuts and bolts.
Any good to you?