So I have just picked up a series 3 2.25 petrol 1981 that sat for two years however with a charged battery starting up straight away with a quick turn over and drove home (just). I swapped the old points ignition for an electronic ignition (Lucas 45D) and a new ignition coil and we have a very nice spark on spark test however now the engine barely turns over (not quick enough to fire) and with a sluggish rhythm and doesn't sound healthy at all. Its not the battery as we tried to jump of a pack and a car and both made no difference to turning speed. With all the plugs out the engine turns much better but thats just because of compression. To fit the electric ignition I removed the battery and im wondering if maybe i might have nocked something or maybe accidently loosened a wire or something? it doesn't seem to be an earthing issue as it started brilliantly before and since then the only thing touched is the battery, ignition coil, electronic ignition and new spark plugs and oil change. Any ideas?

check the battery is good, what voltage with ignition off/on/cranking?

Starter motor?

Double check battery earth connection, both on batt and on truck. Also clean and tighten the power connection at starter.

And make sure the timing is the same as it was (or at least, correct). If it's firing early, it might slow the crank speed down further, and prevent starting.