A standard RS turbo Series 2 box gives 23.5mph per thousand in 5th. This is exactly 70mph at 3000 or 112kph. The standard speedo is a little fast, so will probably show 120kph. It looks like you have the Series 1 geabox, which is lower geared.

The standard 1.6 CVH geaqrbox has a 3.55 final drive, which gives 120kph at 3000rpm.