I am about to give my engine a thorough jet washing and was going to paint it whilst it was on the engine stand.

Can anyone recommend a good engine paint that will stand the test of time?

In gold if possible. Yes... I know.... tart I hear you say. I want it to look good too... gold seems favourite to me.

I would not recomend painting it after jet washing it yes it gets all the thick off but there will still be some oil deposits on the block and you will get spots where the paint has seperated.
I would get it shot blasted but if you do not want to do this (got to blank every thing off) you can hit it with the wire brush in the drill use a number of wire brushes leave one in some thiners to brake down eney deposits then swich over evey now and again.
then i would give it a good wipe down with some thiners (what ever thiners you use for the paint) and then let it dry off then wipe down with a tack rag.
I painted my old XR3 block like this.I got my paint from my local car paint shop they can mix eney coulor you want they just mix the right pigment in with there high temp paint base and it lasted ok.