Kits include screws and instructions. New individual solenoids are replacement parts, so I don't see a problem with it not including mounting screws. I am surprised the Summit listing did not specify. The screws are listed on Summit's website as ZEX part NS6522, with sizing as 10/32 thread. Double check it and get some locally.
The solenoid can be mounted in either direction, so inlet/outlet is where you want. If you are concerned with the label facing backwards, the large nut on top can usually be loosened and the outer cover with label turned where you want it. If memory serves, and knowing I have experience with NOS brand only, the solenoids are electrically nondirectional. Choose a wire for ground side and the other is activation power.
