Valve adjustment Z650 B2 1978

wrote:

I've not heard of a fix to recess wear othe than custom made oversize buckets. 

You don't need custom buckets.
The old common fix is to machine the bore to take stock GS1000 buckets which are larger , convert to shim on top and use the matching larger 29.5mm GS shims too.
Or you retain the shim under and use the now readily available GS1000 under bucket conversion kit.
Kibblewhite Shim Under Cam Buckets-spare-parts-motorcycle-online-uk (suzukiperformancespares.co.uk)