I've done the procedure that festival above talks about, except that I put an Odessey Racing battery inside the case. I've done this on a few (maybe 10 at most) batteries that are in some of the nicest Camaro & Nova restorations. One of my batteries is presently in the most famous 68 Z28 Camaro Stock Eliminator car...but I'm not bragging.....
I've only worked on batteries that hace been dead & dried out before I gut them. My local battery dealer takes the guts for his lead reclamation after I soak it all in baking soda to neutralize the acid. I will say, the "no maintenance batteries", are the easiest to gut.
I showed one of my battery conversions to Rick George (former Rick's Camaro owner), and he thought it woud be a great business venture, but he doubted that I could get away without getting in trouble with licensing companies & patent infrigment....so I dropped the whole idea.
There is a thread on this site that has a picture of a gutted battery for an early Corvette.....I beleive it was converted to hold an Odessey Racing battery.