heat resistant isn't really needed on either the engine block or bonnet (definitely not needed on the bonnet)....
i've painted boat engines with regular bodywork synthetics, painted a goldwing engine with clear over a metallic basecoat and some years ago i used to strip and tart my old 750 honda up every now and then, the barrels,head and cam cover got sprayed with Hermetite engine laquer (an oil based brush paint) that i thinned with celly thinners and put ONE good coat on (you can't put a second coat on with celly thinners in that paint)...
the most important thing is to make sure that the items you're painting are scrupulously clean and have a good keyed surface, the only bit that should need a really high temperature paint is the exhaust manifold, loads of folks use barbeque paint on thier bike downpipes, some VHT paints are not brilliantly petrol resistant if not cured properly :( ....
these are only things i've done and not for recommendations, if you aren't satisfied with the finish it's not my fault
