What I done done before if the upper steel part is rusted out were it bolts to the inside of the cowl, I have taken any 68-70 dash and cut the spot welds -were the top of the dash and the underside of the dash is spot welded together and a few spot welds on along the sides and a couple were the defroster ducts are and separate the top from the bottom,/underside is...and just replace the top, they are all the same. I have done this for customers a few times.