There are enough variations with Seiko that will make your head spin, without adding ND into the equation.
I have a few variants of Honda gages of unknown fitment and at least 3 variants of 400/4 gauges with different faces.
What I noticed,
60 mph seems to be at the 12 o clock position regardless of the max number printed at the top of the scale.
You can't fit a tacho internals to a Speedo base, screw holes don't align.
Calibration is the same for Honda, Yamaha and Kawasaki Speedos. Tachos differ, honda being 7:1
Seike gages have different sealing rubbers between the top and bottom parts and some top (black) parts are 1.5 mm different in height to compensate. Completely screwed me up trying to mix and match the best bits from the junk box.
Regards
Dave