Hi Tim,
I have a friend who owns a MGB and I helped him with one or two restoration jobs on the car. He painted the engine and used e-tech engine enamel. I remembered the name as he gave me some bits and bobs at the time which were in the cardboard box the paint tin came in.
He swears by the paint and seeing it a couple of weeks back it looked as good as the day he painted it which is over a year ago. I just checked Tim and put "engine enamel paint" into ebay and you can find it there, 250ml tins in various colours.
I have never used the paint and can only tell you of my friends experience with it, but it may help.
Ron