I’ve finally got around to doing the 30 minute X axis - or so I thought, turns out I’ve actually done the 60 minute mod 
Top piece is 12mm x 3mm aluminium, drilled and countersunk for M5 screws. Bottom piece is 32mm x 3mm mild steel bar, drilled and tapped for M5 screws. The most difficult part was making sure that the holes, especially the tapped one, were in perfect alignment so the Makerslides could clamp together nice and square.
Not sure about the 60 minutes, took me the best part of yesterday to drill/tap the two bars!
More images of the job here. http://imgur.com/a/Re4tN