Agreed 100%. A good friend runs a resto-mod shop and his rule of thumb is that the actual rust covers an area 4-5x of what you can see blistering. In his shop, I'd guess $25-30 k in body work for just the rust - but he does high end cars mostly ...Absolutely, but the considerations aren't any different than for aluminum heads (1FZ) or aluminum radiators.
It'd be cheaper than paying someone to repair the old rusty steel tub!!
NO 