I'd have to go along with Nifty's take on the situation. I taint no expert here Strato but the thought just crossed my mind that this problem is similar to the one that I just had. I picked up a filter at a swap meet that had the inlet in the front (left) of the canister and found that these were mounted to the rear of the carburator on the later engines to give clearance to the low mounting of the Air Cleaners. On the earlier or Advance Design trucks the steering gear is in the way but the Air Cleaners are mounted atop the carb. Here they have to mount the filter in front of the carb. This requires that the inlet must be in the rear of the canister to put it closer to the tapped outlet in the block.
Denny Graham
Sandwich, IL

Denny G
Sandwich, IL