That's a very tough factory ask, Outlaw. I have a lot of ISN 721 (5/16" x 3/8") and ISN 21 wrenches (5/16" x 13/132") and even they're not under 4" OAL. My first thought was ignition wrenches, because their configurations are a tad shorter than engineers wrenches due to the oppo angles (60*, 75*, and 90*), but none of my 7/16" x 1/2" are under 3-7/8", and the electricals (with the 90* obstruction angle) are the same size on both ends. My next thought was loom wrenches, again, because of the "S" style and 22-1/2* angles, but again, shortest is 4". Kit wrenches are pretty short, but they all go 7/16" x 3/8" and 9/16" x 1/2".
I don't know what the application is, but if you find a wrench that meets the OAL, an option might be to widen the milled openings, which will likely be smaller than you need.