TomD
Looks like 35 degrees to me. It isn't the lowest end of the low. If it is 28 in cad then leveling it up will add degrees. And yet it clearly isn't 45 degrees. I have a 35 degree bevel down plane and it looks reasonably similar. I suspect if you start to draw it out, you will quickly narrow it down further, like say 30 won't stay within the block, or leave too little aft of the block.

If you cut up a 4x4 to basic dimensions, then cut the ramp area totally out. Then you made a few ramps at different angles. One could do that in less time than all this typing is taking, and it would quickly zero you in. You just shove the angles into place from the back. This is not an attempt to make a working plane, just a quick and dirty mock-up.

For instance, I made several Jack planes as an exercise. The first one I made is really an excellent plane, but I made the handle a little too high, and the blade a little too low. with the result that the blade runs into the handle and gets in the way of adjusting. The plane took a certain amount of time to make, and I would have saved all that time if I had roughed it out in 2x material. Most of the time was in carving the handle.