Ahh yes, the joys of working on corroded parts: Athough this particular example isn't down to our lousy weather/salted roads, as you said working on cars that have spent their life in California (or Japan) can be so much easier.
Like I said earlier, (unless you have your own mini-workshop) a good machine shop should be able to do this far far easier and to a better standard than is possible at home.
I agree with others comments about not even attempting to use an unmounted drill - it will go horribly wrong and probably cost you your caliper/s or fingers. Even with a decent drill press it all relies on getting the caliper mounted perfectly and the clamps on most presses just aren't meant to hold something like a caliper.
I thought you might be somewhere in the back of beyond and have no choice but to do it at home but in Glasgow/Clydebank area there must surely be a few small engineering companies who could do this.
In your shoes, I'd exhaust all the other options BEFORE setting to it at home: Googling around, why not give somebody like Forrest Precision Engineering Ltd a call - they seem to have the right kit and their reviews specifically mention manufacturing parts for an old car, so they're not phased by one-offs.
Or try West of Scotland Engineering, like Glasgow 911sc suggested - though they look a fair sized company, so maybe less willing to interrupt production.
If they can't/won't do it, maybe they know somebody who can & will. Any decent shop will need to cover their costs no matter what, so there'll no doubt be a minimum charge but it will probably be worth it just to save the stress.
Just discuss exactly what you're after and what they propose to do before hand, so there won't be any misunderstandings or nasty surprises (like the over-sized nipple issue mentioned above) :thumb:
Let us know the outcome
