After reading this set of posts I contacted Rog to get a set of his bump stops. Fitting took about an hour or so, and after a few drives I’ve set the gap at 36.5mm

Bought a set of internal callipers from Axminster Tools, and then use a vernier to measure the gap. Found this easier than using blocks of wood.

Still get the odd bang, the roads in rural Lancashire can be pretty poor, but now it’s 1 to 2 a trip, rather than 1 to 2 a mile! The road between Bacup and Hebden Bridge is guaranteed to provide plenty of suspension noise.

When we get some fine weather going to try closing the gap by a couple of mm

Very pleased with the results, and Rog’s help and advice was most useful - thanks.