Some questions about vehicle construction

I have this so far:

I’d like to extend it one downwards and add boards around the back, but I don’t know how to take the free space from the front to the back and how to build roof and boards over wheels.

I tried removing the front, then it centered, but when I put something on the rear, it moved one tile up. It’s really annoying, is there any way to fix it?

Is there a way to edit cars with notepad, or something?

I’ve managed to solve it by moving the front one ahead, one tile at a time. I decided to make the cab longer. Suck it, game! (Please add the option to change it’s position on the construction screen.)