I would like to add, this just a block, no probe involved. I don't think my cheap and basic controller card can use a standard touch probe so this idea of a block (adjustable in hight??) To just set the bit hight is easier to work with and avoids messing around with changes to the z zeroing in the cam cad software.
So the idea would be to zero the X/Y with the endstops, install the bit in the spindle with said block holding up the bit at a specific height, then tightening the bit in the spindle, remove the block and you have zeroed all the axis. For tool change, go to home, remove the bit, install the next bit, held up by the block and tighten the bit, remove the block and off you go!
Seems like it should work....
:-)