It won't hurt a thing. The outer edges of the oil pan will kind of dig into the tops of the 2 x 10's, and the oil pan bolts bear most of the weight. I think I remember reading in your resto thread that you are waiting until after dyno day to paint your motor. So that will alleviate worries about skinning the paint on the sides of the oil pan. The motor will sit on the dolly, and never move while it's in the back of the truck. You could add some eye bolts thru the lower few inches of the 2 x 10's and use criss crossed ratchet straps across the motor if it makes you feel better. I do that myself.....but I do have a tendency to swap flies with a bazooka! :D