The recesses under the seats are described on p. 67 of Noland's book - about 6" deep until about #12,000, changed to 2" deep thereafter, and eliminated entirely for 1964. The photo on that page shows them exposed and painted like the jack/storage compartment, with the carpet cut out around them. Nobody seems to know why they're there, and there was never a tool kit of any kind released. I don't have a '63 JG, but there should be something about them there.