Thanks all for the info and thoughts. I've spent hours today going through a piecing together the history of #347. It seems she's had her troubles! Well I can't afford to now dump and run so in for the long hall and to get her sorted and enjoyed I hope!
Given she's effectively now had 3 engines i'm hoping my latest issue is not relating to the internals. Though I have some niggling doubts over the engine map and the last engine rebuild/install as having had her on the ramp yesterday at my mates garage there's some tell tail signs of a rush job and/or negligence. Such as power steering leak due to clips broken and a bracket completely missing leaving things to move around (a lot!) and joints seeping. Also bolts missing in a few places on initial inspection! Will be giving her a through going over now to sort these bits and a detailed look for anything else.
I'm thinking the plan of action based on what I know will be:
1. Check the exhaust/cats for damage/blockage. There's plenty of chance given her history of running issues they have been damaged along the way. I did hear on my first run and hard(ish) pull a metallic type rattle sound where I initially thought something metal like a heat shield had fallen off and was dragging under the car but it stopped after a few seconds and never returned. This may have been a cat giving out but I did not get a running issue at that time and just hoped it was a one off quirk, or belt slipping and making an odd sound (ignorance is bliss... well at least initially!). If a cat has failed we can strip it out and see how she runs then. Effectively de-catting her has it's appeal anyway but will have to worry about the MOT later!
2. Next will be seeing what the plugs look like and replacing if required. If they are in poor condition it will raise further questions but worth initial investigation.
3. If neither of the above are successful then it'll be a compression test.
4. If compression is good then coils maybe. They all seem to be ticking away so doubt this will be a cause at this stage.
5. Check fueling is ok.
6. Will get a code reader on her as well and check for errors.
5. My next consideration is whether the map is any good. My mate/mechanic is experienced with mapping and does a lot of Jap tuning but I have read that Dreadnought have invested a lot in mapping S/C ZT's. However i'm not sure they'll map an install they've not done? They are also a 500 mile drive to the other end of the country, though if I can get her running satisfactorily a road trip would be tempting!
One other question I have is for S/C cars, would there be an expectation they should have an up-rated Head Gasket fitted or is standard considered acceptable. The invoice on the paperwork I have for the last install/rebuild says Head Gasket kit but that's it. I am going to call the garage up to see if they can give me any more detail. Thanks.