A regiment would normally consist of some 600 to 750 men. If you think of a unit as a company size unit and ignore its name as being a regiment, grouping four companies (regiments) of line infantry and one grenadier company would give you a standard regiment. In that case a 160 strong line unit would be most realistic.

Or you should by a HAL 3000 computer, ignore the pathfinding problems and mod the units size to 600 or 750 men