Billy, i think that it´ll be all good, with that Ford Dark Blue engine paint.
I don´t think a specific paint was used through all the years anyway, since colour does variate quite a bit inbetween the engines here.
What you should do though, is to ensure that you´re "cheap" when it comes to paint.
If you coat it too genorously, you´ll hide the sandimprints on the casting, and make it a smooth glossy surface, which they never had originally.