Struggling to mount rev counter coupling

[bendik]

I am converting from a Vic Camp style rev counter drive to a cam drive. I recently bought a rev counter coupling but I am struggling to align/mount the cam cover. If I lay it flat the cover is too high for the mounting. If I align the holes the cover stands proud of the head.
What am I doing wrong? Is the coupling too long? Should the slot in the cam be deeper?

[Jon Pegler]

You may have bought a coupling for a Ducati bevel V-twin. That coupling is longer than the single cylinder one.

[bendik]

Starting to suspect that as well. Lacey/bevelsingle didnt have in stock for a while so bought from somewhere else..
Will measure tonight. How long should the single one be? Is it correct that twin one is 13mm long?

[Jon Pegler]

The single cylinder coupling is 11mm long.