CS Grant's various scanarios and Tabletop Teasers are often set out in generic Horse & Musket terms but they generally provide a sound basis for a good game in almost any period. One just has to exercise a bit of judgement to translate for different periods, scales and rule sets. I generally use of one 3 methods to do so.
WWII is one period where I have often used his scenarios and teasers. I have done so using home made rules and 10mm troops, Rapid Fire and Storm of Steel in 54mm and Blitzkrieg Commander (BKC) in 20mm. (I have also played using both Command Decision and BKC in 12mm but I didn't set those games up.) The best approach for each varies but one or the other generally works.
1. Points: The simplest and least satisfying solution. In the version of Sawmill Village which appeared in Scenarios for Wargames, players were instructed to pick 6 units from a list of available troops. This implied that all were of equal value. The notes at the front gave no particular size but said that cavalry and light infantry were assumed to be about 1/2 the size of line infantry and that batteries were 2 guns. If one consults the very 1st Table Top Teaser, it is made clear that the units involved are those laid out in Charles Grant's The Wargame, and a points value is given, but for years I went under my first assumption and it has worked just fine.
The way I work this is to take the number of units per side and multiply by a suitable constant to get the desired size of game. So for example, for the scenario just played, the defender has 2 guns, a cavalry unit and 2 infantry units in town for a total of 4 units with 7 more in town as reinforcements. The attacker has 14 units. If using BKC and multiplying the number of units by 100 we get a game where 1,400 pts attack a force of 400 pts on the hill with 700 more as reinforcements. For a larger game, simple increase the constant and multiply by 150 pts x number of units or even 200.
Simple but it does allow players to choose a completely different ratio of infantry to guns to cavalry/armour and possibly change the feel of the whole thing. . Leaving WWII I remember playing the game with Romans vs Parthians using Armati. It was hard enough for the Parthians to attack the hill, but it was even harder when we switched sides and they were tasked with defending it! If you don't have a point system to work with this doesn't help at all.
1.5. Allocated Point This is just a variation on the point system but it gets around the issue of inappropriate forces. It can be awkward though if the point system is too far out of whack and some judgement is required. Basically its a matter of breaking the points down by troop type.
So, for the scenario just played, using BKC or similar for a small game: (warning I haven't looked up the pts for a sanity check as to what it provides)
On the hill: 100 pts of A/T guns, 200 pts of infantry (and infantry support such as MG's and mortars), 100 pts of armour
In town: 100 pts of armour, 100 pts of recce, 400 pts of infantry, 100 pts of artillery (could be off board)
Attackers: 200 pts of Heavy/Medium Armour, 100 pts of Light Armour, 100 pts of recce, 800 pts of infantry & infantry support, 200 pts of artillery inc A/T guns and off table guns etc.
Command may either be drawn from available pts or issued free based on reasonable proportions.
2. Standard Units. This only really works if everyone is on board or you are setting up the game with your troops on both sides. Since the original teasers were designed for standard units, its just a matter of adopting standard units for your period. If one side has a quality advantage this can be balanced out by larger units.
Its been a while but we used to use something like:
Infantry Unit: 3 stands of infantry + MG or Mortar
Guns: 1 antitank or offboard gun per scenario gun (2 per battery) or maybe a dive-bomber for a few turns
Light Cavalry Unit: 3 light tanks, armoured cars or 1/2 tracks
Heavy Cavalry Unit: 3 medium tanks, 2 heavy tanks or 1 really heavy tank. (Depends on the .period and army). If the medium tanks are greatly inferior add an extra.
Light Infantry. A fudge factor, might be a recce or 1 1/2 track with 1 stand of elite troops, or 2 stands of paras or similar.
I say stands, they could be sections, platoons, or companies, depending on what rules you are using. Guns are assumed to have appropriate transport.
Lets say we were doing mid-war Russians attacking vs Germans. Perhaps:
On the ridge:
1 HQ 2 A/T guns, 6 infantry stands, 2 MG,
1 HQ 3 STUG III
1 HQ 3 Mark IVH,
1 HQ 6 infantry, 1 MG, 1 mortar,
1 HQ 6 infantry, 1 MG, 1 mortar,
1 truck with 2 stands of Panzer Grenadiers with enhanced firepower (extra lmg),(attach as desired)
1 FAO for 2 off table 105mm howitzers.
1 HQ, 1 recc stand, 12 infantry, 1 mortar, 2 MG, 1 45mm ATG,
1 HQ, 1 recce stand, 12 infantry, 1 mortar, 2 MG, 1 45mm ATG,
2 76mm guns or maybe 2 SU76,
1 HQ 3 stands of SMG tank riders, 6 T34 76, 3 armoured cars or light tanks.
the same principles apply to ancients, renaisance etc.