Right, so, thought i'd update this post as we've 'fixed' the problem and all the advice really helped...
So, found out a valve seat in the head had slipped (luckily didn't cause any damamge somehow) and that the other valve seats were loose. Replaced all of these, refurbished the whole camshaft and head and it was running better.
We then took the car to a friend who looked at the timing and balancing of the dellorto carbs and it's running incredibly well! Idling so smoothly at 700rpm give or take.
We then came across a little problem with the ignition coil, we thing that either something is 'wrong' with it or there is a loose connection... It runs pretty well again after some fiddling around but i don't feel particularly confident...
So let's buy a coil and see where that gets me. I think perhaps a 280Z coil? Thoughts? Just spoke to Mike who was concerned my car might have a ballast resistor and so (correct me if im wrong) the standard 260z coil might not be working to its full potential.
Advice wanted please! I have a day to order a new coil on next day delivery befor we take to Le Mans and it'd be great to feel more conifent in the car before we go! haha! i think it'll make it there either way but yeah safe than sorry etc.