Here are a PC and projector I recently ordered myself to build a new AR Sandbox. I haven’t tested the projector yet, but it seems the best replacement for the old recommendation, BenQ MX631ST. It is a wide aspect ratio projector, meaning it will over-project towards the left and right once aligned, but that should not be a problem.
PC: Something with a medium-range CPU such as an Intel Core i3 or i5, and a medium-range NVidia graphics card such as a GeForce 1650 or GeForce 1650 Super or better. This is not an endorsement of any kind, but it is the PC I ordered: HP Pavilion gaming desktop
I chose the Core i3 version over the i5 version because it comes with a better graphics card, and GPU performance is more important for the AR Sandbox than CPU performance.
We have a BenQ MW632ST and it has worked well with our AR Sandbox. As you say, it over-projects the box edges. But the sandbox calibration compensates for that and only black is projected outside the box.