K40 Adjustable Focus Head-Quick focus guide tools

When I bought my K40 Laser machine (one of the MANY chinese clones available on the flea bazar) I decided to overhaul it from the start.
It has never been used with the Nasty cracked software or even had the main pcb powered up. It was all removed, totally re-wired and is now powered by a grbl "cnc" nano controller and has 255 grey scale engraving capabilitys and also a few new Safety related UPgrades, Water coolant flow Switch, Door open switch, digital cooland temperature & Current displays, you know all the important stuff that should have been included from the start but was never installed due to chinese profit margin and tight pockets.

I also upgraded the mirrors and cutting head, and that is were a little problem showed up ! how do I now set the correct height. The head is focus adjustable & most of the tools on Thingiverse would not fit or be usable, time to do some measuring and calculate the distances so I could print a nice easy to use guide tool to help me set the corre