Thunder bird 60-66 may be right. You want to make sure the seat backs are tall enough to just be seen at bottom of the window. It will be a hard choice I’m sure. May i ask whats wrong with the 40s seat?
Keep the stock bench seat. Or, use stock 40 Ford split front seat the was used in the "opera coupe". Modern buckets will make it look like a street rod. Here's the split seat for sale: https://www.fordbarn.com/forum/showthread.php?t=226039&highlight=1940+ford+front+seats
Well it is not a street rod but I am not trying to make it an original either. It has a fresh 47 engine build but it does have 4 wheel disk and different front axle and 8 inch rear with 4 link.
When I was still wet behind the ears, my brother and I bought a Forty that had been through the hands of someone who chaneled it and lost the running boards. It had a pair of Jeep seats in it. It was a slick little rod, eyes flipped on the springs, and ran like stink. Those seats were as minimal as could be. If I were building a one today I would take my tape measure to a Pickup, SUV salvage yard and select a bench seat from a Colorado or Dodge medium sized up, or whatever would fit the Forty application. Most have the driver side separate. In something that was a narrow seat as a Forty, you will appreciate the extra space on the seat. As far I know no one in their right mind wants to sit in the space behind. Unless you want to carry children. For that you need a woody, or a sedan. I could be saying everything you don't want to hear. But, riding in those Jeep seats was a pain in the memory. A little luxury on a long drive goes a long way toward having a pleasant experience along the way. No if and and butts about it.