I was going to throw a small block chevy back in the truck, but.... I've been looking at the 'W' series big blocks 348 409 427 motors, more torque and power plus they look great with those scalloped valve covers,it'll make a nice rumble too.Dress it up with some finned aluminium valve covers.
like this:
http://www.edelbrock.com/automotive_new/mc/manifolds/images/409_engine.jpg
