The dash has nothing to do with the structural parts of the cab. It appears that GM built cabs without a dash and then installed either a Chev or GM dash with spot welds. I use these kind of bits to drill spot welds.
http://www.dentfix.com/viewItem.asp..._Weld_Drill_Bit_for_High_Strength_Steels I have the Spitznagel drill, but if you are going to just do one project, you can use any drill. The bits appear on eBay ever so often. They are also sold under the name of Würth. They are all made in Germany and make other spot weld bits seem like toys.
