1940 dodge coupe retrofit rear seat

I have a 40 dodge 5 window coupe my young fellow is 10 and always wants to come along to the shows etc i currently am driving a 36 chev 5 window coupe with a small bench behing the buckets he is getting to big for it I am working on a 40 dodge there is almost 12" more room on the rear I am trying to find a rear seat I can start with from something newer that is thin but can be fitted in the rear. some of the newer sports cars do not have much room but is survivable if you are a kid. Anyone have any experience in putting in another seat from a newer model in something similiar

Thanks in advance for any ideas

 

Been told a lot of the 70s/80s Mopars have the same size rear seats, dart, ect.

 

I know where I can take some measurements from one of those

thanks