Here is a suggested basing plan for the Government Army at Auldearn. As with the Royalist plan, the figure count is based on the Auldearn OOB listed below at a 1:10 figure scale, adjusted for use with the Warhammer ECW rules. Pike to shot ratio is listed in the OOB - I have used 1:1 for raw levies, and 2:3 for government raised regiments.
A detachment of Buchanan's Regt was present at Auldearn (the rest of the regment remained on garrison duty in Inverness), and I have given that a pike:shot ratio of 1:1 to give a reasonable number of pike models. But this detachment could also be fielded as 20 commanded shot models with no pike.
Campbell of Lawers' Horse is too small at 30 troopers to field as a WECW unit at 1:10 figure scale. This would be only 3 models, so I have combined Lawers' Troop with Drummonds to give a single unit of 130 Troopers, or 12 models at 1:10 with 2 ranks.
However, if you prefer to field these two horse units seperately in penny-packets, as they were in reality, you could split them into two units of 5 and 8 models respectively, or even 6 and 7 models. This gives them at least some limited staying power to make a contribution to the battle using the WECW rules.