I will be interested to see a photo of the finished surface.
Regards
Steve

Good to see one that's close to original and not covered in pattern parts.
Regards
Steve

You can try Coventry Boring but specify that the surface needs to be as smooth as possible from the grinding process otherwise you will encounter brake chatter from braking at speed.
Regards
Steve

If you haven't already got one purchase a Clymer manual.
Check that the damper has been assembled correctly on previous strip downs.
The washer that is shown in the photo that has been under the fork cap is not an Z1 OEM part.
Regards
Steve

The grease will show either end of the swing arm where the caps are.
Regards
Steve

What make are the pipes?
Regards
Steve

Was a genuine new seal fitted to the ignition housing?
Regards
Steve

The chain adjuster stoppers came black as standard on the bike but the spare part was with a BZP finish for you to paint.
Regards
Steve

If it's been stored face down then it's probably the needle damping fluid that's run out which I think is glycerol. It will need attention as without the fluid the needle will bounce.
Regards
Steve.

Graham,
You are not alone, I purchased an UK, August 73 registered Z1 and found quite a few parts missing and some engine bolts had been sheared at some time in its life and glued back in place will high temp silicon!!
Regards
Steve

Does anyone out there offer a complete Z1 wiring harness finished with the black,gloss sleeving where appropriate rather than an insulation tape wrapped finish?
Regards
Steve

Turn the tap half a turn anticlockwise before lifting the tank off.
Regards
Steve

Procure as many NOS parts as you can, it may be more expensive but there are plenty of restorations out there loaded with pattern parts.
The original parts are out there and it’s all part of the process.
Regards
Steve

Invariably this will be caused the damping fluid within the unit drying out.
Regards
Steve

To go to an original NOS unit is quite expensive at around £400 and after laying around for maybe 40+ years is an expensive gamble.