Thanks all, the cut out is instant and I didn't notice anything odd in the tacho, other gauges or warning lights but - in the event of a repeat will certainly remember to look at the tacho.
A good checkround found nothing loose in the ignition electrics (or anything else obvious) and in only one of the failures had ther been any significant shaking (over the level crossing) and I've been over miles of rougher road than the other two times.
Having only recently had the luxury of a working speed / mileometer I had allowed the tank to run lower than before hence my preoccupation with the level, since I bought it back in Feb I have had some heavy trailer loads and passenger loads on without a moments hesitation from the engine and despite the larger size it does not accelerate like my 2L lpt Wentworth but once up to speed it load lugs just as well so doubt it is anything like a clogged fuel filter but did wonder if it mught be pulling the odd air bubble somewhere in the tank part of the piping ??
Regarding the boot strut anchorage, there is a significant amount of force on that stud and having hands and fingers which are not of the delicate artistic type, unless I can find an open route upwards from the light cluster access and glue a nut onto a 'ferret' rod it looks like I may have to drill an access hole to get a nut back on
Its been raining too hard to have a look today.
Cheers & beers for your time and knowledge
Rick