But I'd like firstly to actually see all of them...
Easy to do. Choose one and open it with gpicview. Click the (+) magnifier button [fourth button from the left] to enlarge the view.
By the way I'd like to have a diagonal-direction one.
I'm tempted to ask why.
Open one of your choice with gimp or create your own. From the menubar, choose Tools > Transform Tools > Rotate >>> type in the angle you want (example: 45 will get you a 45 degree shift) - type <Enter> - click the rotate button. Click File > Save As > give it a name and an extension type (png or jpg) [Important: do not try to use gimp native - xcf - extension].