The spec is usually cast into the drom somewhere - maybe not in this case being mil-only item, though.

As far as the three screwd aligning the drums, I'm on that list. I can't recall a pilot bore on the hub that would otherwise do the aligning (some swear it's tehre - maybe a running change in production?)

Anyway - the machining cost to countersink the holes, cost of special screws, and teh general PITA factor leans more to them being needed, not just a "convenient"way to retain the drums before the wheels are attached. Remember these trucks are "lowest bidder" items, so every cost-cutting measure wouldhave been taken that could be thought of. The layout, machining, and necessary quality-control for these dang holes just seems excessive unless htey were mandatory fro drum alignment.

So there.