Scrap and wire brush the heavy stuff off, then use a degreaser to rid the block and head of trapped oils. After that step I wipe things down with lacquer thinner just to make sure things are really clean.
All of the "engine" paints I've used have come in quart cans and I've painted with a brush...they flow out great and look like they were sprayed when dry. One coat has worked for me most of the time, but no harm in putting on a second. I also paint after the engine is fully assembled with all the parts that get painted the engine color.
Good luck!
Mike B
