Just an update. The Strombergs needed a good overhaul (in my opinion) so I purchased a pair of reconditioned HS6 carbs. They've been fitted and barely tinkered with and the old girl has never ran so sweetly. Not fussed about extra speed but she pulls superbly and is much more responsive. I'm a happy bunny! To be honest, a big part of the running problem I think was down to the lack of heat shield, there's a lot of heat coming off the stainless manifold. I haven't fitted one yet but have had no issues with the new carbs.
Not going to go much further with it other than tidy up the porting and gas flow the intake. The head will come off over the winter as I don't know if it has been converted for unleaded and I may get the crankshaft balanced at the same time. Then I think it's off to Tom Airy (thanks Haggis) to get her tuned.
Might be ready for a couple of shows next year!