I have a 240z that at some point in its life had the right front frame rail and tower replaced (professionally and correctly). But it is missing the plate that id's the block. How can I find a list of vin# to block numbers?

I hope someone will correct me if I'm wrong, but if that tag is missing, I don't believe there's any kind of database that you can cross reference to get that data. I think you might be out of luck.

I agree with rturbo 930

The best you can do is locate a car with a similar VIN and see if the engine installed in each has a similar number. Even that is not conclusive because the engines weren't installed sequentially...

No previous paperwork for service history? No original Datsun Service Booklet with the Z?

What is the VIN on your 240Z?

http://www.zhome.com/IZCC/ZRegisters/classic.htm