Tj, what's commonly called pickling in plain carbon steel manufacture uses hydrochloric acid to remove mill scale, other acids and blends of acids are used on other alloys .... iron oxide is rust, the result of flushing with water after the hydrochloric bath, the phosphoric acid [sold as 'rust converter'] converts that iron oxide to ferric [iron]
phosphate, which is protective to some extent, but needs further coatings to really do the job - if your frame had any surface rust on it, there was no 'protective layer' on it, the reason it doesn't have real corrosion is it's a higher carbon steel that the mild steel of that hoist frame .... you could treat the whole thing with phosphoric acid after you clean it but it'll last at least as long again as it already has with no treatment other than keeping it off the road in winter
OTOH, the resto-pack doesn't specify exactly what treatment was used, the phrasing could mean that GM used hot rolled steel [that had the usual hydrochloric bath at the steel mill], and when they stamped/cut frame members from it they further 'pickled' it with a phosphate bath
Truckrolet, you can make it official if you come up with some written info from GM stating frames were painted semi-gloss black, the fact that you've seen a couple or a few that you think look painted says nothing about the many hundreds of thousands of TF series trucks produced at a dozen different plants over a 5 year period - I've parted out a lot of these trucks and am sure most, if not all, have never had any paint on them
Bill
