Hello Ralph,
just ask the official Nikon Service in Germany whether they can reprogram the N70 for the leader-out option.
I know for sure - because Nikon service had done it for me and photographer friends of mine in the past - that this has been possible for the Nikon models
- F90 / F90X
- F80
- F100
- F5 (as the F5 has also the classic rewind crank for manual film rewind and is counting backwords when rewinding having the leader-out is always possible by manual film rewind).
But I am not sure concerning the F70. Just ask them.
The F6 has fortunately this option already built in: You can choose between the two options
- leader-in
- leader out
after automatic / motorized film rewind.
And as the F6 has also the classic rewind crank for manual film rewind and is counting backwords when rewinding having the leader-out is always possible by manual film rewind, too.
Best regards,
Henning