1980 Z1R D3 wrote: And if not how bad is the undetermined mileage going to hurt the value of the bike?
If someone is being honest with themselves, it shouldn't matter at all. These bikes are 40 years old, and it's nearly impossible to verify the true mileage. There is no car-fax type record for these bikes. My blue Z1R has about 45,000 on the clock, but I have a box of speedos in the basement. Give me 30 minutes and it'll have 15k.
On the other hand, I can't think of any better way to remind a potential buyer that the true mileage is unknown and unknowable than by having an obviously not-correct speedo.
The fact that you know at least 30 years of the history of this bike probably matters a lot more than the number on the odo. Knowing the history is pretty rare. And what matters most is the hard to find or Z1R specific parts and the overall condition, specifically lack of corrosion and oxidation. From the pictures your bike looks to be above average.