Do you mean the Tudor Sedan or a 2 door Victoria? I may not be correct but I believe they were different until the Tudor came out in a Deluxe model. The later Victoria seats matched the 400A and the Deluxe Phaeton. I have drawings from the 1990 Victoria Bustle thanks to Vern Schwebke I can send if these are the seat bottoms you are asking about. It has seat bottom sizes for both the early and late seat bottoms and springs.
The plywood seat bottoms are sold by several vendors but EXTREMELY pricey for a piece of plywood with a few holes.
Your name was a clue you just might mean the Victoria.
You are right. I have a early Vickie. (Feb.) It came with seats but they are wrong. That have the prong post to the floor not the three hole adj. type. I may have to use them for now, just trying to ID them. Thanks ED