Welcome Johnny.
Let's see if I can answer some of your questions. First, PP does not necessarily mean stock. It means more like stock appearing. You can do any internal modifications you want as lang as it appears stock, including boring to 1350. But, you must also have stock mufflers, carb, air cleaner, frame and ride height. If you lengthen the swing arm you will be in the M class. In M you are limited to 10% over stock wheelbase. Once you move out of Production class to M you also move to PG class. So, with your described mods you would be 1350 M-PG.
On another note, there is no M-PG class at El Mirage. You're either P or A. The 1350 A-PG record is a pretty good one. There's a couple of us running at it.
As everyone says, keep reading the rulebook, then read it again. Good luck and see ya out there.
Larry