|You can make the two disks use one drive letter by making them a dynamic disk. Look at the link below for more on that topic.|
I do not see any advantage to you doing that. The primary purpose of a dynamic disk/array is so the same path can be used while expanding the capacity of the drive letter in use.
In your case you can just change the path of where you want to install or store stuff. No need to combine them. There are disadvantages. If either physical drive fails, all the data is at risk.