some call it a crank girdle, and yup its cast iron. D you come up with some wacky ideas don't get too caught up in theory - a CA18det in a 1000 would hammer. 320hp at the wheels a series?! you might get away with running no girdle but i'm not sure its worth it. You could save weight in manifolds, good light (evo etc) intercoolers, maybe flywheel, you'd probably add weight with the alloy sump. all this taken into account (if its for the 1000) it'd probably struggle to go around corners well and all the tiny steering and suspension parts as well as the body itself might likely bend.

other than that its not a bad idea

I saw your wagon out at the workshop the other day. why don't you show it off more?