Since you are not stacking boxes you may be able to adjust inside height at top and bottom to give bee space. A 1×10 is only 9 1/4 inches wide so you need additional space above and below.
There's the reason they used the larger wood.
I am making medium supers, 6-5/8", therefore I have to use 2x8 boards which are only 7-1/4" wide.
Seems like a waste yet the lack of quality wood these days makes this work out for the better because I trim both
long sides and the edges are often pretty bad allowing me to get decent pieces out of them.
Untreated Southern Yellow pine is what I am using and it heavy but sturdy stuff.