Well, today I finished the job off by replacing the plugs and HT leads, checking the timing, and I soldered and heat-shrunk the temporary joints on the amp to distributor cables, and took it for a run. What a difference! It runs *much* better, much more perky, more responsive, quicker, just better all round
On the slight downside it has now thrown a little exhaust manifold leak at me (where the manifold joins the downpipe) so while that's a pain to fix (if it won't nip up) at least it's not a brain challenge!
Thanks again everyone for all the input and help and suggestions, much appreciated, it was really helpful!