speedometer tach housing help needed

[boxer]

well i think i don't have everything i need to properly mount the tach in the housing.
i have two holes in the back of the housing that look like bolts would go through to attach the tach.
nothing lines up on the tach to match up to the housing where it would/should bolt to the back.
is there an internal brack i am missing or were the tach and housings changed up at some point.
thanks
marc(almost there)