Here's the deal: I made them for myself; that being the case, I didn't worry about how to make them in quantity. This means that each is handmade, of course. The bits needed for each seat are:
1 sheet of 1/2" hardwood plywood (actually 1/2 sheet would work)
4 pieces of 20 gauge galvanized sheet metal, about 8" x 16 " each. All are brake formed to make the required seat angles.
Poplar wood strips: 3/4" x 2 1/2" wide x 48", 4 per seat. They are all chamfered, using a table saw.
strap iron (steel), 1/8" x 3/4" x 48": 5 pieces.
a whole bunch of 1/4" bolts- some 1" long, some 2" long, with nuts and some washers. These hold the seat bottom parts & the seat parts together.
some 5/16" x 1" stainless steel cap screws. These are hand "machined" on a drill press to form a polished, domed head, using a grinder while the drill press rotates the cap screw (bolt).
10 threaded 3/8" thread brass inserts, to be fitted to the seat back/bottoms, for attaching the seat brackets,using the 3/8" SS cap screws.
some 1/8" plate steel to make the side angles from. The ones I made for myself were from 2" wide bar, cut and welded to shape. If I were to make more I'd use my pattern & have them plasma cut from a solid piece of steel. Cheaper, better, faster. Unlike NASA. I powder coated tham.
A leather hide. One large (55 sq. ft.) hide is enough to do 2 seats. If a half hide is purchased, it's a $200 extra charge, but as the whole hide is $400 it doesn't make sense to buy only half. I buy my hides from Douglass Interior Products in Seattle. Excellent quality (they're especially made for custom aircraft interiors- the hides are from Scotland, vat dyed. Many, many colors & textures available. Custom dying a new hide to match can be expensive.
foam padding. This supplied by the upholsterer, who does the final upholstering of the leather seats.
That's about it. I could probably make a seat (or two) in about a week, plus the cost of upholstering- about $1200 for the pair, leather not included.
There's nothing really difficult involved for the home handyman, just normal mostly carpentry skills. A table saw, drill press, electric grinder, electric drill, and normal small tools. And a week or so. Plus a very good upholsterer, familiar with leather automotive seat upholstery. The leather uses a combination of sewing, zippers, and velcro to assemble the bits and fit them to the deat back & bottom. The side bolsters are stapled to the plywood.poplar frames; the center sections are removable (velcro) and are openable, to be able to change the foam padding , if necessary (zipper)..
The completed seats are attached to the front seat mounts only, on pivots, which are made from 1/8" x 3/4" steel bar, with welded legs to raise the front off the deck. The rear mounting holes in the seat rails are not used. This means that the seats can be removed in about 30 seconds each, as only a quick-remove pin is used, fitted with a spring clip. The seats can also be tilted forward, until they touch the windscreen.
If someone wishes to try it themselves, I'll be glad to send the dimensions of what's required, along with a sketch of how they're assembled. The tricky part is the pattern of the steel side brackets, which must be followed exactly in order for the seat to fit the car. The side brackets could also be made from hardened aluminum, to save weight (they're heavy!) but would cost a bit more.
The materials would cost around $200 for the pair, which does NOT include leather, upholstery, cutting or welding the brackets, or else having them plasma-cut (a digital pattern would have to be made, take a few hours) and of course powder-coating.
It would be more expensive to make only one, of course; more than half the amount for two, in part because of the cost of leather, but also for reduced economy of production. It would still take close to a week for just one. Lots of running around; actual making of bits is not the most difficult or time-consuming part. This is true in almost any type of production work.
If I were to be asked to make one or more seats, I'm open to offers. Figure a week of my time (40 hours or so), with all the running around including working with the upholsterer, ordering stuff, cutting, assembling and so on.
Could they be designed using different materials? Of course, but that would mean starting over- new patterns for either formed/welded metal, fiberglass, whatever. Some wood would still be needed, to attach the leather cushions, etc. to (remember they aren't made from tubing, which most stock seats are made from, that use steel clips to attach upholstery to!) and the brackets are still an essential part of the design- the brackets are what make the design work, as the seat upper & bottom cannot be attached directly to each other, due to the crossmember. A stiff leather flap conceals the otherwise exposed crossmember, which is covered in carpeting. Not strictly necessary, but looks better.