I'd have another look at Maguras. I ran HS22's for years in the mid 90's when XT v's were launched as you couldn't get hold of them for love or money. Pick up a nice pair, try them and you'll not lose money if you hate them and flip them on.
Once you get used to them they are epic in terms of stopping power, and they aren't necessarily the "on/off" modulation that the trials boys and girls love them for. Hardly needed any maintenance either, which for a retro build is less of a consideration - but for a regular rider in the winter muck of the south downs was a godsend (unless you had a habit of stacking and ripping the hoses out, which I did, and was more than a little inconvenient)
A set of racelines don't have to be lairy yellow (I'm sure I've seen silver) and they are more adjustable than the lower end models. I'd use them on the Zaskar rather than your steel bikes and always with a brace as they can flex the seatstays (visible even with a brace!)
Problem with the emergent disc brakes of the mid 90's is they were just clunky massive things (though Formula were quite smart IIRC) - and no one really wants to bolt a rear disc mount onto the seatstay of a boutique steel frame... AMP did disc brakes too, so why not an F1 fork on the steel frame with their disc.