Two additional things. When you have the carbs off always check to make sure the floats do not have holes and therefore leak. Over rich will cause bat performance as well. Lastly every one checks plugs, spark and king wire ( coil wire). But I have had the carbon button in the distributor fail. This is very hard to find if you don't suspect it.
Rollsroycerescue. Good luck.
You can find the correct cap and rotor as well as many other parts at Flying Spares, Introcar, Alber's, etc. You can also go to the Bentley heritage site, Input your chassis number for the correct parts as delivered.