Don't make me throw this thing!
I think I'm also confused by the statement in 5.1.3 that discusses leg units that have DP and AP capable crew-served weapons attached, which I took to mean the separate heavy weapon counters such as HMG, SPG-9, etc.
Is 5.1.3 referring to the counters that show a crew manning a weapon such as a grenade launcher (again, Scenario 2 has this), and if so must they be attached to a squad/section or is that something else again?
I can see on the SM-8B data card that a number of crew-served weapons are listed, but I'm having trouble relate that to the various counters.
See the unit images and labels in 1.6.1 for clarification. The easy answer is that if it's a large counter (i.e. the same size as the tanks) it's a Towed unit (see 5.2). There are 5/8" markers that show MG or ATGM sections as you mentioned - these are infantry and the noted weapons cannot exist apart from the infantry carrying them.
Does that clear it up?