Try a Revell Miter box, 10$ +/- on Amazon. It is a manual thing not the micromark powered jobbie, but it may be what you want. should be able to get one at any hobby store. I got mine at MIchael’s arts and crafts.
Thank you all for your knowledge and suggestions.
Dobson miter ordered. Hopefully I can cut straight I beams finally.
Here is another useful product I bought to square things up after cutting - handy when needed:
The Northwest True Sander
Tempted to say you can approximate the functionality of the True Sander by cementing a piece of sandpaper carefully to one side of a razor saw and then working its ‘back side’ against slot faces in one of those miter boxes with ‘wide enough slots’ to clear the as-glued thickness.
This will likely NOT work with the overhead-suspended design as there will be enough lateral deflection to cause vertical effective beveling.