The brake rotors (that are rusty from the car sitting for 25 years untouched) that are on my 71 240z say they should not be turned down below 10.5mm. They measure at 10.5mm.

Is this likely because they have already been turned or is this the original measurement? (For what it's worth I already ordered new rotors so this question is largely academic - when I get them I'll have a better idea what to expect from new)

Mark

Standard thickness new should be 12.5 mm with a wear limit of 10.5 mm. Total deflection new should be less than 0.15 mm and parallelism should be less than 0.03 mm.

Your 10.5 mm rotors are at their wear limit. They wouldn't happen to be the vented hat type, would they?

They wouldn't happen to be the vented hat type, would they?

Not sure what a "vented hat type" is... but I THINK these are standard, regular-old rotors...