I'm pretty near finished painting the engine in my '54 3100. Bolting parts back on today. Painted in the truck.
I used dark grey engine enamel paint from
http://www.fillingstation.com/.AEROSOL #FS-359 $16.50
PINT #FS-119P $39.50
QUART #FS-119 $69.95
< CLICK > for a recent discussion.
< CLICK > for pics of original engines (B&W).
< CLICK > for discussion on cleaning the engine.
If you are painting the engine while it is in the truck, spend time planning your schedule. Seems like I wasted a lot of time masking off areas multiple times as I needed to paint other items.
Good luck.