So my tfi failed in an impressive way incl big back fires and then dying completely, I replaced it with a second hand unit and it started and ran which is great, however now it has a miss at idle and on take off intermittently, I think the second hand unit is breaking down, does this sound about right?

have you done anything to the dizzy? like replace it too?

Check your coil for cracks, vacuum leaks, worn dizzy bushes, and HT leads n plugs.

It has new bosch leads. I replaced tfi again with brand new unit stopped missing apart from very intermittent miss, it did play up the other day and not want to start so but is fine now so I'm thinking Coil, love the car just working through these issues, other than module and coil is there anything else that would cause an intermittent starting issue in these motors? Seems from what I've read there's surprisingly a bit to the electrics

Whats the fuel filter like ??? What fuel do you use in it ??? Have you gone over the bolts on the Intake Manifold and checked them for tightness ??? Have you checked the MAP Sensor hose ???, as they are prone to splitting/cracking down at the manifold barb.