The guy I used to blast my cab started with soda first, then went back over it with more abrasive sand on the rusty parts. I was worried about warpage from the heat that sand builds up in the metal. The blaster said that these old trucks have thick metal that can handle it as long as the operator is aware of the possibility of warpage and is careful.
My suggestion is to use soda over sand except in the really rusty areas. I'm taking my hood over to him this weekend and I am demanding that he uses soda. There are other types of blasting media as well, such as glass, plastic and walnuts. Ask what they use.
