I cranked out this 27mm high riser-block from a piece of 35x100 mm aluminium bar today.
The 6mm holes in the corners are for attaching the block to a standard breadboard or optical table that has M6 threads on a 25mm pitch. There are four holes in each corner in a 12.5-by-12.5mm square pattern. These allow attaching the block with 12.5mm 'resolution' both along X and Y.
The middle M6 tapped holes are for attaching to a translation stage. The stage is old with a weird 34x92mm bolt pattern.