Might as well not even bother, if that’s the case.
Check the math with your local EE. Even a trivial 6” pigtail greatly reduces the effectiveness of an SPD. Make those leads 18” long and the device will never see any surges. That’s why it’s so important to mount them directly to the bussbars.
At this point I’m inclined to omit the SPD and let the inspector call me on it. Code has no business requiring things that aren’t available.
