how did they get away with it?

5000rpm is significantly over 100mph in overdrive top... 100mph is more like the straight 4th speed (gearing approx 20mph/1000rpm). The 123GT had a 4.3:1 rear axle.

thanks bob, great to see another aussie on here, real cool to see that you have teh came car as me too, a 67 122S, is yours 2 or 4 door?

I've seen an indicated 117mph too, on an Autobahn a few years ago, when visiting a friend in Duisburg. Without a tacho, I'm not 100% sure of the revs, but I think it was about 5750 rpm in o/d 4th - wouldn't be brave enough to do that in normal 4th with the estate / o/d diff ratio! Took plenty of road to get there as the acceleration tails off above the ton (aerodynamics - what aerodynamics?!!) However the front left tyre blew out 1/2 hour later but fortunately I was only doing 70 / 80 when that happened....