The two sheet metal cleats on the bottom of the seat cushion wood frame are about all that keep the seat from moving. I really don't know what the two closely spaced riveted clips with the X marks are for. Ford purposed that compartment for other storage uses but I can't say much more than that. Cars came with jacks, tool rolls, & other stuff but I don't know if those are related to that or not. I took a quick look at the Ford Model A Owners Instruction Manual to see if there was any mention of the space and really wasn't all that surprised that it mentions nothing about tools or the jack at all. We all know they came with a dual purpose hand crank & lug nut wrench, a tire pump, plus the tool roll and jack but there is no mention of any of that in there. I guess Henry figured that the owners would figure it out on their own. Coupes & commercials used that space and the tudors had a space under the back seat for all that stuff. Open cars used the space for side curtains or tools with an additional under floor storage on the phaetons as well.