I really need to pin down a visit to the garage it’s in.
Yes, very nicely restored and original survivor Z1's are now becoming very rare worldwide and fetch strong money (e.g.this restored low chassis# at $45,000 -
https://www.motorcyclesunlimited.co.uk/1972-classic-kawasaki-z1-900-for-sale/ ) and most are now going back to Japan as in recent years they have lifted their home market ban on bikes over 750cc (in 73 and 74 Kawasaki produced the rare Z2 750 for the Japanese market and not many made it overseas).
A 'rule of thumb' guide:
Mid 72-73 - Z1 model (black engine (polished cases), barrels and head (polished fins and cam covers))
74 - Z1A
75 - Z1B
Mid 75-76 and 77 - KZ900-A4 (known as the Z900 in UK, Europe and ROW)
77 - the KZ900-A5 rolled off the production line in Lincoln Nebraska for US market.
Cheers,
Andrew