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[Ishootforblood]

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[Rob112o]

Just looking at pic 1 I can tell its 90s-early 2000s. There should be an etched serial # the first 3 digits will be year month.
Far as pellets go I always order online as big-5 is way over priced. The big5 in my area recently started stocking the .20 Benji cylindrical pellets. Order from a site called Pyramyd air. They do the buy 3 get 4th tin free. The Benji and JSB are the way to go.
That's a walnut stock. Since it's a Crosman made Blue Streak you can see the similar design that your 392 has. So you got a walnut before they went to the cheap hardwood.
The pump arm could be due to a previous owner over pumping it. Which requires more effort and causes improper pumping technique.

[Rob112o]

Nice work brother! If the stock is still off a little and it bothers you. It did for me on many of occasions. Get yourself some of the small felt stick on dots. Add them to the inside of the forearm. Obviously, add them to the side that will adjust the forearm in the direction you want. Now in the closed position it will make the arm sit straight with the butt end. This will also quiet down the rifle during pumping.

[Rob112o]

There are 2 parts that Tim has that I absolutely love. His front end plug and the steroid lever. Both are rock solid, should I say steel solid. I've managed to get power up to 18.39 FPE on the cartridge 392 and C9A with only 8 pumps. So I don't need the steroid lever as I'm not over pumping like his steroid rifles need (14pumps)to get max power. Regardless, his lever is very nice!! It really adds heft to the rifle. For my keeper rifles I'll get his steroid plug. It's a well made solid piece.
So here are some pics of the lever. I lined up rifles that you have so you can get an idea of what you need to do. All the holes are at the same distance apart regardless of model. The left rifle is a 392pa. The middle is a 392P with the steroid lever. Right is a C9A.

Notice the middle lever is solid as oppose to the other being hollow.

Steroid lever