SpoonColors is right about the gumbo making really good soil if you mix in some sand, mulch, manure, etc and can get it broken down. You should also till in some gypsum. You can get it at any garden center and it breaks down the gumbo clay.
And do not try to till gumbo if it is wet unless you want to clean the tines about every foot you till . Damp is OK, but if it is too wet it will load up the tiller spines like crazy.