Hello Paul,
Temperature itself is not an issue on the engine block. Most paints will withstand 300 degrees F of heat. If your engine gets that hot, you will have much bigger issues to deal with !!
The high temperature engine paints are mostly for exhaust manifolds and exhaust systems which can get 1500 degrees F or more !
Now what is most important is that a good engine block enamel be chemical resistant. It must be able to with stand gasoline, coolant, oil etc. Most automotive or industrial two stage enamels and/or urethanes work great. Auto parts stores or paint supplies should also have single stage paints in spray cans for engine blocks. The single stage spray cans will work but are not quite as durable as two stage systems. As with any paint, if you are spraying it over bare metal use a primer coat first. The primer will improve the adhesion betweent the paint and the bare metal, and will keep it form peeling off in the future.
I see that you are in the UK, but look on "The Eastwood Company" website for more information on these kind of products. I am sure you will be able to find some product near you.
