thanks so much for those diagrams are really helpful I've struggled to find anything like that that makes sense so that clarified things a fair bit!

I went out in my break to have a look but it quite hard to see without taking the washer bottle and other plastics off and I only had 15 mins

I closed off the check valve so made it as standard and the vac dropped to -20 and then when revving the engine at a couple of times it made it vibrate to what seemed like near stalling so I don't know whether or not that's too much or too little air and I couldn't rev it and see what the actuator was doing ... id like to think this would throw up the engine management but it doesn't seem too...

the actual plunger itself hasn't been changed just the valve controlling the vacuum..

I also found a video on youtube with a chap testing the vacuum control valve and he refers to there being 25 inches on the primary of it so if anything mines lower than that!