I know I’m being a bit lazy by asking before trying, but is it possible to remove the back pad without removing the seats? This is a late model ‘73.

Even if it is, would it be worthwhile to remove the seats?

I noticed I neglected one of the clips and some of the vinyl could use resecurng.

No, regardless of model year. Yes.

Just pull the seats! It takes what 1 min each?

Learn how to remove your seats. You need to know that anyway. Jeff was being generous, it literally takes seconds to pull a seat once you understand how the rails release.

Move the seat toward the dash. Hold the spring down with your finger. Pull the seat forward off the track. I'm slow. Takes me 10 seconds.

Maybe his seat rails are gummed up and very difficult to slide....many are.
It's difficult to get leverage to push forward.
I've had to get down on my knees outside the car to get any movement....
Look at it as a maintenance benefit.

I hadnt figured that out
I have been unbolting mine and lifting the whole thing out (what a muppet)

when mine were gummed up, I had to sit in it and slide it forward with my weight. It's also easy when your sitting in it, to use your fingers to push up on the safety levers, to get the seat off the rails. Also if there really gummed up, just get the seats far enough forward to get to the rear 10mm bolts (socket size) and remove the seats with the rails. Once out I laid the seats on a bench on there back and used a rubber mallet to remove the seat mounts. I only had issues with stuck seats with aftermarket seats.

You don't need to remove the seats. Push them all the way forward. Push down on the backpad. I did this just the other day while working on the roll bar pads. I pulled the backpad to clean behind it.

Right you are. You do not need to remove the seat to get the backpad out but it seems the OP might be having seat issues too. So removing them and cleaning and greasing the tracks might be in order. Plus taking the Backpad out and putting it back in w/o seats in place is so much easier and a great opportunity for some deep cleaning.