I decided to concentrate on the unstayed rig type for simplicity and  I am hoping to try out at least a balanced una rig with a "Z bend" mast ( similar to the one on Avalon)  and a wing sail  (used very successfully by SailBuoy on a previous Microtransat).   On previous model yachts I used to struggle to figure out where to place the mast. I have seen some models with two or three separate mast slots, hence the ultimate solution, the  mastbox., which  allows adjustment of the fore and aft mast position over a wide range. Each rig fits in place using a "cassette", ( basically just a rectangular block) which slides into the mastbox.

Here is a pic of the mastbox being glued in position. To get it vertical, firstly the boat was clamped to the bench by the keel and adjusted so that the keel was vertical checked with a spirit level placed on the side of the keel.  The mastbox itself is a 20mm wide slot, so I inserted a 20mm diameter  tube into the mastbox slot and then checked that was also vertical side to side using the spirit level.