In part, this depends on what the dummy engine is made of. If you're talking about a resin casting or vacuum formed ABS you'll need to do it one way, and if a plastic WB kits another way. Here's how master modeler Tom Pierce did it on his SBD Dauntless:

http://www.renderwurx.com/rc/SBD/htm...ding/dummy.htm

(This site is an absolutely priceless source of scale-building info, BTW. I just wish it were available in book form so I could thumb through it!)