I think standard car cylinders have a tandem piston arrangement - i.e providing two separate pressure outlets (at least when the pedal is depressed). See this link:
http://auto.howstuffworks.com/master-brake.htm
I'd assumed the rover part was similar but with a commoned fluid reservoir inlet.
Tilton do a master cylinder that looks like a tandem (demontweeks sell tilton stuff I think)
http://www.tiltonracing.com/content....ist2&id=22&m=b
Maybe give your local SVA centre a call and check with them?
Richard