Ply Gem NW Pro Classic size 3052 Pivot Lock shoe

It's very difficult to say with any certainty what you need without seeing pictures of the original hardware, as this can vary irrespective of whatever manufacturing info you have. That said, it sounds like you need T-Lock Shoes like our 15-195, 15-195B, or 15-194. I have seen plenty of Plygem windows that use these T-Lock Shoes; the problem is many older windows have shoes have a characteristic groove shape in the stem that lets them connect with a similar groove in the channel balance. Our shoes and balances lack this interface, which means you would not only need new T-Lock Shoes, but new balances as well. See our Series 795. Again, I can't be any more definitive without actually seeing your hardware, but look all this over and see what you think. 

As I feared, it looks like you'll need to replace both the balances and the old T-Lock Shoe. If the metal channel is 28" long, then yes, you'll need our S795-28. I really can't make out the T-Lock Shoe from this photo, but if it's 1-1/4" wide, then its likely our 15-195, which comes by default with our Series 795 balances. Keep in mind you'll need to choose a stamp code too, which designates the weight this balance is meant to support. Look for a stamp code somewhere on the metal channel. If there is none, or you are uncertain, obtain the exact weight of your window sash. You can match that exact weight with one of the weight ranges listed alongside each stamp option on the product page.

If the window is exactly 18 lbs, you really can use either 18B or 18C as the stamp option. If it's towards closer to 19 lbs, you could still use either but I might just use 18C to be safe. Still, either would work if that's the exact weight. 

I believe your second question is about pivot bars. The 15-194 is often used with the 26-021, but you want to absolutely make sure that's what you have in the bottom corners of your sash to be safe.