Recently I replaced two 19" outboard monitors with two 22" widescreens.
macOS provides a utility to set the arrangment, however there is no way to know how well you actually line them up (I wanted the bottoms of the two outboards to be at the same coordinate)
Norman provided an idea which worked out quite well, and I have expanded on it.
Here is Xojo source code for a VIEWER (you need to use the system utilty to change them), but it reports all the relavant information
Note : This SHOULD work for Win10 as well