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Not an exact answer to your question, but....I found vinegar leaves flash rush.
Naval Jelly leaves a type of protective coat, but only for a few days.
These were for parts not going to be painted - window regulator and door latch mechanism.
If I were going to roll it either way, I'd roll it forward on the firewall like someone else did. It's stronger and you don't run the risk of dinging up that really large smooth area of the back of the cab. Of course, you also have to tie if off or prop it up so it doesn't roll back on you. Also be careful of the cab corners as you might damage them by rolling the weight of the cab on them. If it was an option for you, would you be able to raise up the cab on the stand you have now, to the point where you can get under it, or slide it onto a couple of 4x4s or something like that where you can leave it upright and still get under it to blast it? Even if you can set up a stand to one side and move it over to work on one side, then slide it over to work on the other. Just a thought, there are no doubt many ways to do this.
If you have enough manpower to lift it off the stand (I assume that's how you got it there in the first place), then it's probably no big deal to set it on its back gently.