I assume you're talking seat springs/cushions?
LeBaron Bonney was the source and repop originator for Model A seat springs. They're gone now but others have stepped into the breach.
Before you take the big step, consider buying a seat bottom, but only the covering for the seat back - if this is possible.
As you buy and use the completed/stuffed/prepared cushions for the pickup trucks, the first thing you will notice as you sit in the drivers seat is how close the steering wheel is to your chest. People in those days simply were not as "large" as they are today - plus our "expectations" of space in an automobile has changed. We are simply used to driving more roomy cars (not to mention cup holders.)
I say buy the partial seat setup because you can use the seat bottom quite well, but a lot of larger drivers can benefit from a "thinner" seat back in the trucks. You take the prepared cover and using a piece of plywood as a back and 3" of foam to the same outline you fabric cover the foam and staple the cover to the plywood back. This is then used in the usual position giving the driver a more modern "feel."
Now this issue may not be a problem for you. Perhaps you're into judging, or unlike me you're not 6-3 tall. Or maybe your driving expectations are different than most. But it is (or was) a "users" option in the L-B days.
Another aspect which comes to mind with original format seats is that they're stuffed with padding certainly, but L-B used to use a layer of "granulated" filler which self-adheres certainly but can be pulled loose. Otherwise known as the "perfect mouse-insulation material." Mice, if they can access your car interior, or even if they can't, will remove the stuffing to be placed elsewhere - as in any confined space. Like your muffler, or your No. 3 engine cylinder where the exhaust valve was left open when the engine stopped the last time. (tell me how I know about these?)
My original format L-B truck seat cushions live in a large footlocker sized wooden storage box when they're not being used as protection against mice. This is a MUST DO when parking the car even for a few days.
Foam, on the other hand, is relatively mouse-resistant (not total), and can be bought in different "durometers" to effect different degrees of seat cushion. Your back might be made more cushy compared to a seat bottom which probably wants to be a bit stiffer.
Some suggestions from a "user."
Joe K