pulling dents with pennies

My son and I are rebuilding a 91 chev p/u and it has some haildents in it. We are going to have to paint it so we thought we would pull dents out. I was reading a book and it said you could braze a rod to a penny size piece of copper and solder to body and pull dent out. Did not tell me what kind of solder. Tried silver solder didn't work. Does anyone know what kind of solder? Is it acid core etc? Percentages. Thanks for any help you can give me.