Have you verified those are extensions? On an Advance Design truck it's the complete hub that is different.
I know I've had this discussion before, but no one has ever convinced me the Task Force trucks have a bolt-on extension instead of a dually hub.
Plus the trucks I've seen apart from the 60's and 70's have a complete dually hub.
On an AD truck it's the bolts that hold the brake drum in place that make it look like the 'extension' would unbolt, but really all that unbolts is the drum.
Can you post some pictures of yours? I sure could be wrong about this, but until you take it apart and show some pictures I'll remain a doubter.
