My bro in law has a nice set of calipers he's offered me, however they're bolt on and my current (vintage 80's) brakes/frame run recessed calipers. Is it difficult (or not advisable) to set them up on my frame?
I thought possibly yes, but obviously don't want to risk them falling off mid hill descent!!
Any advice, redirection to elsewhere, appreciated.

Take a couple of short recessed style nuts and drill the threads out then file the heads down so they will fit in your fork and brake bridge flush acting as a bushing.

Then you can mount the nutted style as you would normally.

Thats a very good answer Otis,I totally agree with you !

8mm drill and you're good to go. Did it my '83 Trek 600. No issues whatsoever.

I drilled the fork in the back side only. The rear brake bridge is more difficult to do it that way, so I just drilled the whole way through. The rear brake does so little work in overall braking that I'm not worried about any minor movement, but it doesn't move anyway.

edit: maybe I should learn to read

Thanks for the info guys.

Thanks Bob, I did that for the missus' bike, but this is the other way round. Bolt on being fitted to a recessed frame.

Or rethread the center stud/cut and mount recessed. Short center stud nutted rear should fit front as recessed, turn long front into short recessed rear. You may be able to switch out the center studs if the brakes are the same design.

Rivendell sells an insert for $1 if you don't want to drill out recessed nuts.

Thanks again. Always useful here.

Since I screwed up my response the first time, I'll tell you what I've done in your situation. In fact, I did some DC 500G G's tonight.
1. Measure the center bolt length and thread lengths you need and mark it.
2. Thread on a 6mmx1 die and cut threads down as far as you need.
3. Cheap hacksaw to cut the bolt to length.
4. File to clean up the end.
5. Back the die back off the center bolt - you're good to go.

Takes all of about 5 minutes.

You need something like this:

Like I said, Rivendell sells an insert for $1 if you don't want to drill out recessed nuts.

That picture is lifted from the Rivendell site.