Hmm, could have sworn the OP said he clearly heard a difference, knows what he wants, and is just looking for a way to mark or reference to be able to easily return to that azimuth when swapping carts. That's it, right?
I mean, he did say "for quick switching so I can at least eyeball the angle".
It's hard to say without seeing the arm and how the head shell attaches but what you want is something with one or more reference marks on the head, and one or more reference marks on the arm tube. Simplest/cheapest will be to cut two strips of paper, put some marks on it like every mm, tape one to the head, the other to the arm. Fold and trim so they line up where you want.
I did something like this on my Conqueror tone arm. It had VTA but no marks to calibrate so no way of replicating different VTA settings. I used a label maker, trimmed the label down real thin, taped it to an acrylic disc, and you can see how great that turned out in my system pics. Look at pics #15-17. https://systems.audiogon.com/systems/8367 I would try something simple like tape and paper first, then if you like it maybe make something better looking/more durable like I did here.
I mean, he did say "for quick switching so I can at least eyeball the angle".
It's hard to say without seeing the arm and how the head shell attaches but what you want is something with one or more reference marks on the head, and one or more reference marks on the arm tube. Simplest/cheapest will be to cut two strips of paper, put some marks on it like every mm, tape one to the head, the other to the arm. Fold and trim so they line up where you want.
I did something like this on my Conqueror tone arm. It had VTA but no marks to calibrate so no way of replicating different VTA settings. I used a label maker, trimmed the label down real thin, taped it to an acrylic disc, and you can see how great that turned out in my system pics. Look at pics #15-17. https://systems.audiogon.com/systems/8367 I would try something simple like tape and paper first, then if you like it maybe make something better looking/more durable like I did here.