Kind of like only being able to count to 9 7/8 in stead of ten? Don’t put your finger where it doesn’t belong! Dr. couldn’t understand that one.The shims ought to be available from Dorman, also the correct bolts and related hardware.
Strongly suggest the use of a heavy chain wrapped around the coils of the spring and then around the frame rail and secured with a bolt and nut before using the spring compressor tool. Even the best of tools can pop free and having the chain in place means the spring will be constrained as to how far it could fly. You do not want to eat a spring. Too much iron is bad for your health!!