For what it's worth, I agree with IABSM, but I modify it for solo play (I like to play 'against' the bad guys, not simply 'play both sides to the best of their ability').
As mentioned a couple times, Platoon Forward is a must, it maps out scenarios and enemy forces for you, it's fantastic for solo gaming.
The only other difference from 'normal' IABSM is to help out with the 'unknown' enemy (Plt Fwd's blind system, as opposed to the normal blinds): instead of using cards for individual units/Big Men (as per IABSM), place generic 'enemy' cards in the deck as they are spotted. When an enemy card comes out, come up with three enemy options and roll a D6:
1-2: Most Dangerous Course of Action (whatever the worst thing the enemy could do to you at this point, carry that out).
3-5: Most Likely Course of Action (what's the thing you'd most likely expect to happen? This is different from MDCA as MDCA is generally a high risk/high reward option, while MLCA is the norm).
6: Least Likely Course of Action (nothing too crazy, something that makes sense, but is 'fortunate for you').
Mind you, you've got to look around the table for a minute. Let's say there are three enemy units on the board, and you have one of your infantry units moving up a road followed closely by a tank. One of the enemy units is an infantry unit at the opposite end of the map, one is an enemy infantry unit dug-in watching your friendlies march up the road, and the third enemy unit is a tank out of LOS of your friendly tank on the road.
MDCA is the enemy tank pulls out into a firing position and engages your tank.
MLCA is the enemy dug-in infantry unit opens up on your infantry in the road.
LLC is 1) activate the enemy unit at the far end of the table, or 2) the dug-in enemy unit sees your tank coming up the road and decides to fall back out of LOS.
This will make your enemy much more effective, off-setting some of the 'player bias' in solo games.
Also, as an, ahem, experienced solo gamer (I don't have any friends ;) ), I'll tell you part of what has made solo-gaming so much fun for me is 1) playing one side against the other (not 'playing both sides,' this makes me feel like a spectator), 2) having mechanisms to mix up activation and not allow me to do everything I want (IABSM is perfect for this), and 3) streamlining all the other mechanics to keep the game straight-forward and moving quickly. My personal experience is that you can easily get bogged down if there is too much to remember/look up with shoot/move/morale mechanics.
If you're going to go with IABSM, it has some fantastic concepts for firing, moving, and morale, using with elements (squads and teams) using varying amounts of dice to fire based on the situation, squads getting between 0 and 4 actions per activation based on training, experience, and shock, movement affected by shock, how many actions are used, several differing types of terrain modifier, and ultimately controlled by rolling dice, etc…
What I'm getting at is that I think those work like a champ in two-player games, but can be a bit much in a solo game where you have to do all the thinking, calculating, remembering, and looking up for both sides. At least starting out, I would recommend paring things down a bit, as suits your needs.
For me, I don't use individually based men (you're talking about a company per side, so roughly six thirty-man platoons, plus support), I use one-base per squad. All rifle squads get two actions, squads move 'x' inches per action, squads fire with 'x' dice per action, with very simple 'to hit' and casualty rolls, simple shock effects, and simple rallying. If I were you I'd start simple and build up. Or do like me and stay simple ;)
In my humble opinion, the blind and activation systems are the heart of IABSM and what sets it apart from all others.
There's my two cents.
V/R,
Jack