Tom,
I agree with the above on gettin it blasted ...mine was COATED an I mean coated in old bondo ..only after blastin did we find what it was hiding ...my metal was BEAT up but sound ..an after seein WHAT we had ..it was the process off bangin out dings an dents ...some spots like the bottom of the doors needed some lead to fill the pin holes , but at least we knew what we we dealin with ...made life allot easier .
If you are dealin with a questionable base as you stated ...in my opinion you will be hounded later down the road when the body work you are questioning fails ....
As my Pappy told me years ago ...IF YOU ASK YOURSELF THE ? OF WHETHER YA SHOULD 99% of the time .. YA JUST ANSWERED YOUR OWN ? ...YA SHOULD .
Just my 2 pennies
Tim