ADJUSTABLE I don’t know if anybody has made this but anyways this is what I thought about. So instead of getting multiple sizes of fleshing beams so you can fit a tiny mink on one and a big coyote on the other, why not make a system where you can shove a wedge in your beam to make it wider or skinnier. (Solid wedges would be used and made to match the curve of the beam) I believe if done right this would be cheaper than buying multiple pieces of pvc or multiple wood beams.
Should I try to make it or just buy a beam?

I can't see how that's going to work. Go buy a 6" (actual size 51/2") hard wood plank . Tapper the end down to about 2" and plane the edges down to nothing. You can lay rats and mink on top of the beam and flesh them' The beam doesn't have to be inside the skin.

I have one made out of a 2x8. I do everything in Iowa on it from mink to coyotes. Even did a few deer hides and one buffalo hide.

Yeah I’m just overthinking the beam. I’ll just flesh the rats and mink on top of the board or right on the stretchers.

As suggested use a 2X6 cut out in the shape of a large fox board. This size and shaped beam will accommodate all pelts larger than mink, marten, muskrat, etc which are easily fleshed on their own shaping boards. Also build it to fit your height angling up to your solar plexus.
Keep It Simple!

I think your idea would work but be more trouble than making a couple of different size beams.

Wood moves. The shape of the wedges -- relative to the "female" pieces on either side or vice versa -- would likely warp, cup, bow or twist enough to misalign the surfaces over time. In other words, the radius along the surface would not be consistent or smooth as a result of movement. Using a non-wood composite material would be a better choice.

In the end, a one piece or laminated solid beam still remains the best approach when using wood.

agreed, it'll take 4x the time than if ya just made 2 the traditional way.

Been a while since I've caught a mink as Ive not done a lot of water trapping where mink are likely, but I'm pretty sure like muskrats you can just lay mink on top of the beam to flesh. You don't need to fit them on the beam unless you have a really fatty one. For years I've done everything on a narrow beam. Does make things a little slower for the bigger animals.

I don't think it will be stable enough. You won't want it to move around while you are pushing. Got on YouTube and watch Coon Creek outdoors making his PVC beams.

Make one from wood It's much easier to work with and you will get a better beam.

I made my fleshing beam from a 2X6 about 30 years ago. Still using it.
I also made a mink fleshing board from a 2X4.
Simple enough to make. Better than factory made? I dunno. Never had one.
just