You could, but I highly reccomend you not go that route. Its simply not needed. You can easily remove 99% of the rust/dirt/grime without removing anything by using a grinder with a wire wheel or sandblasting. Once its clean you can go back and treat the little nooks and cranies that you couldn't get to with a decent rust converter or phospho acid to neutralize it then prime and paint. I did this on my 57 and it looks great.
By removing the factory rivits you'll have an extremely hard time getting everything back to being square, bolts are not a good replacement for them either. Rivets expand to fill the hole aroung them and hold tighter. Bolts won't hold nearly as well as the original rivits and will allow for extra flex in the frame. You would also have the chance for them to loosen up over their lifetime as well which could end up being dangerous. If you were just moving one cross member to make room for say a gas tank like some do, then bolts are ok, but not a smart idea to do on the entire frame.
Also reriviting the frame wouldn't be an option unless you have some industrial sized rivit machines handy.
Just my two cents.
cody
