...for anyone who's still interested in this saga LOL!
Following my conversation with Boyer the only thing they could come up with, given that all plugs spark, is that one of the plug cap suppressors was below tolerance and that would be enough to cause electrical interference with the digital ignition causing "random retardation".
So - stripped the whole lot back and check the connections. The worst pot has always been No. 2 and guess what - lowest resistance in the plug cap although it was only 7% down on 5k ohms so still theoretically in working tolerance. No.3 was also down at about 6% under and that's the second worst pot for firing.
So, replaced both plug caps with new ones (they were also new!) and they are within 1.5% tolerance across al four pots now. Also replaced all spark pligs (B9EA) with standard B8EA plugs.
I checked the fuel was getting to the carbs and they all tickle up to overflowing nicely....just got to sweet talk the wife to having a go on the starter this afternoon now. If that fails, I'll mothball the CR and build myself the solo starter I've been planning for some time, so I can check and run without having to wait weeks for "the prevailing conditions to be right" to get some starting help. Fingers crossed...
....oh to cap it all (No pun intended) the CB450 has dropped onto one pot on the new ignition on that one (PVL). So - both bikes out with firing problems, great!!