You would probably be better off just buying a new galv chassis, by the time youve stripped it then spent alot of time cleaning the chassis down then re assemble; and you would still have an old chassis which has been galved, with inherited water already in it.
Your not going to get the rust out of the inside, and your chassis will just rot from within, would look a bit better while it was rusting away tho.
If everything else on your 90 has been rebuilt anyway you wouldnt have to overhaul/replace much else; unlike myself and V8moneypit!!!!
Im still trying to stop rust reappearing on my rear axle, after 5 or 6 coats of hammerite!!!
There are often galved chassis on the bay which have been shotblasted and galved so most of the work has been done for you already, think they go for about £6-700.
