I fitted the manifold yesterday afternoon, then left it overnight for the silcone sealant for the front and rear seals to fully cure. I put everything else back this morning then fired it up. The banshee has fled!
I then reset the timing and the idle speed and mixture. It will now idle smoothly at 400 rpm! I set it to 700 though, then went out for a quick blast. That felt sooooooooo good!!! My eyes were glued to the oil pressure, vacuum and temperature gauges, but all was well.
I then double-checked everything when I got back. No oil leaks - so the time I spent thoroughly cleaning and degreasing paid off. And the new core plug is holding the water back OK. Happy days!
Let's hope the sun stays shining this week - I've got a lot of snake miles to make up!
Thanks for your help and moral support guys - a problem shared and all that ......