Byron,
If I do a poor job of cleaning, I was thinking about a radiator shop for cleaning as tcrist suggested. If not, I figured the welder would fill the tank with water and I was thinking about your dry ice idea to boil off C02.
Good suggestions about pressure test and seal coat too.
Add a fuel sump and shut off valve, relocate the electronic fuel pump lower, possibly a Barry Grant fuel sink, maybe some hard line to replace some braided hose, wrap the headers, add a better vent, and I should be good to go for next year's track weekend.
Sounds like a few more buck$ than I thought to do it right ...