I think the only difference between Mk1 & mk2 brakes is that on the Mk2 the rear pulley is Hard Nickle plated - which makes it MUCH more wear resistant - on the outer tooth side and more importantly on the inside. If you can find a local metal plater, getting Mk1 rear pulley’s nickle plated is a really good upgrade. Good luck with the machining - you will pick up many customers on here for that upgrade.