Like someone else says the IPLs at Poulan Pro show 164 and 137 carbs for different saws but the carbs all carry the same part #.
I would be surprised if ordered today that a 137 wouldnt show up.
I had sent an email to walbro a while back asking what the diff was between the 137 and 164. I was told the 164 replaces the 137 which was now obsolete, and the 164 was listed for 54cc and 60cc, the 137 for 60cc Poulans. I was looking for a little more in depth info but as usual didn't get it.