a true baked on ceramic coating would be the best i think, not sure how powder coating would do
as for the rattle can job or any paint for that matter to a certain extent your primer is gonna be what keeps you paint safe... on a engine that is painted the same color as the vechilcle (hot rods and stuff) most of the time there is just a some very good coats of primer under regular paint... now it it won't hold up on headers stuff or your downpipe but it should handle 400deg. no problem... especiall being its not at 400 most of the time
a good high temp primer and some high temp engine black (if thats what color you want) i would bet money would give you no problems at all
if it was mine i would definately give it a shot first.. if it doesn't work what are you out 30min. to remove them again and $12 worth of paint... a lot cheaper and many more color choices
better yet here it is from the horses mouth
duplicolor is good to 1200 deg (i got curious as to how hot the engine paint was good for) so you should be A O.K.