The minimum speed is 43mph now 70kph so he'd be pushing an RM to maintain that speed. It is only a draft idea to go up to 80kph. Best thing is to avoid motorways altogether and stick to main roads as we do, cheaper and safer.

My bus number (if any): RTL 960, RM 1585, RML 2667 and several RTs

The problem is that so many drivers, so-called professionals as well, are completely lost off the Motorway network. I think this man is going to really struggle, there were different ratio sets for the Leyland worm drive diff, however the only ones I have been able to find recorded so far are 6.5, 7.33 & 8.66 all of which will make the vehicle go more slowly. Apart from Foden the worm drive diff had been superseded for Lorries some 10 15 years before it was in PSV. There is an issue regarding the fact that as ratios become smaller numerically the size of the driven gear increases so the casing needs to be larger once a certain point has been reached. I suggest you contact Rush Green Motors Scrap Yard and let the customer do all the dealing at his risk.

Having looked up the proposed legislation in The Brussels Times, The draft wording is that the vehicle should be capable of achieving 80km/h on a flat level road. Not that is HAS to be driven at a minimum speed of 80km/h, otherwise there would be a lot of problems in Belgium once you get across to the Ardennes.

There's a section there heading south from Liege/Luik/Luttich on the E25 that climbs steadily for about 15km. We took BEA MLL738 up there in 2018 and it managed that at about 45km/h in 4th gear and didn't overheat. There aren't many heavies that go much quicker up that hill.

Looking at the figures roy quotes above for Leyland worm drive diffs, I'd suggest that the NG buses must have had similar ratios to the AEC diffs otherwise they'd have been remarkably slow on the road. I doubt there's much difference between the top revs of the AEC and Leyland engines.

My other advice to my client is maybe look at uprating the 11.3 engine t run at 2200 rpm if that engine is capable of running t hat sort of speed. I know the 760 is set to run that fast, but that has a balanced crank and front pulley dampers. Or as Brian says, keep off the motorways!

My bus number (if any): RML2532

It seems very sensible legislation. 50 mph is going to eliminate just about all old buses and some more modern ones as well. The Double deck bus is an urban or inter urban vehicle, it doesn't have a place on the Motorway network, so I think this owner just needs a reality check.