Looks great. You're moving right along. I think you will be able to make a good looking "body" pretty easily. Just add a jig saw to your list. You can go with the plywood idea for the cowl to nail/screw to or use 1.5" lumber. I would extend your floor to meet with the flared bottoms of the cowl and taper it back toward the frame (or straight back to where the frame tapers out). You'll have to think about how to deal with the rear frame where it kicks up over the axle, but that's it.