I was nearly done assembling this post (a post I started when I spotted the useful seat comparison image below) when I discovered that Derek already has a pretty complete post (and frankly better than mine was going to be) on the topic of rear seats (and was the actual source of the seat comparison).

https://www.thecj2apage.com/forums/rear-cj2a-seat_topic34996.html which is an image originally posted to the CJ-3B Page.
But, there were still a few unanswered questions I had after reading his page, so I deleted what I had and reframed it as shown below.
I realized:
1) I didn’t know if the DJ-3A used the CJ-5 rear seat, the CJ-3A/CJ-3B rear seat or something else?
2) And, did the Surrey have it’s own rear seat or the same as the DJ-3A? (My guess, based on the pics above, and Bruce’s pics below, is that the DJ-3As and Surreys used the 3A/3B seat)
Below are photos of Bruce Agan’s DJ-3A restored back seat:
While my DJ-3A came with a rear seat, it was actually one of the folding rear seats from an M-38 or M-38A1, a topic covered in these two links:
https://forums.g503.com/viewtopic.php?t=235427
http://willysmjeeps.com/v2/modules.php?name=Forums&file=viewtopic&t=10636
Here’s a pic of my 1956 DJ-3A with the rear seat that was in it. While no the correct seat, it fit in there pretty well:



































