With a simple trigger, such as you are describing, There should be very little side to side movement in the trigger - "wobbling around". the inlet should be tight and smooth enough to prevent lateral movement, and still allow a smooth swing of the trigger. Forward movement is limited, again, by the inlet in the wood.
It is far better to pin the trigger through the wood, high, as in near the same level as the sear bar, than to use the commercially available 'tabbed' trigger plates that pin the trigger very close to the trigger plate. If you are going to use a 'tabbed' trigger plate, take the English lead and make the tabs high above the plate, emulating the 'through-the-wood' system. A refinement of this type of plate, is a fine leaf spring attached to the plate behind the trigger, that applies upward pressure on the trigger, keeping it engaged with the sear bar at all times. This completely eliminates 'wobbling'. But I do not think that this feature is common on 18th C. longrifles.