Calipers aren't expensive necessarily. Think before you remove steel from your frame. There's appropriate hardware out there.
Yeah, but they are more expensive than zero. This is a well documented method of installing recessed brakes on an older frame, I'm just querying specifics rather than asking for alternatives.
If you put your front brake on the rear, does the thread stick out enough for you to put a nut on it? If it does you could then put the rear on the front. This will involve drilling out the rear of the fork (easier than the rear brake hole), and getting an extra long internal bolt.
Yeah, it does, this is what I'm currently doing. Unfortunately I want to use both brakes, so this leave me without a brake for the front. Running the rear on the front isn't an option, as putting the nut inside the steerer tube simply isn't safe in my eyes.
Or, you could take the brakes apart and replace the bolts with longer ones, which'll work with the old-style frame holes.
Hadn't thought of this to be honest, this could be an option. Still means sourcing suitable bolts though, which could be tricky as there's not much clearance for the top arm over the bolt head, and again, it means buying stuff - I'd rather drill this and not spend money on anything (however cheap).
Thanks for trying though guys!