I'll answer my own questions:
In regards to the two different part 253's, the one that doesn't fit is completely bent out of shape, plain and simple.
I've confirmed that
the blowback chamber jams are caused by the internal hammer-like piece (which I already mentioned, is sticking up about a millimeter too high) getting caught on the back end of the plastic blowback chamber. This problem is solved simply by adding an enhanced recoil spring, which gives it the added strength required to pull the back end of the chamber over and past the obtrusive hammer piece... (which is where the jam occurs). However, this is not the proper solution to this problem, as the hammer will eventually wear through the the cheap plastic chamber.
The problem of the hammer sitting too high when cocked is caused by wear on the part of the hammer where the left sear (part 266) makes contact.

I'm sure this is caused by excessive use of full auto (or just lots and lots of shooting on semi), in conjunction with the greatly increased tension of the enhanced hammer spring (which the internal pieces where not engineered to withstand).
That problem aside,
the reason that full-auto doesn't work is simple enough as well: Ridiculous amounts of wear on the part of the right sear that makes contact with the trigger bar.

When a shot is fired, the impact of the slide blowing back vibrates the internals just slightly, which is enough to cause the trigger bar to slip underneeth the right sear, (which is exactly what parts 260, 261 & 262 [which I removed] are there to do: enforce semi-automatic function).
So it seems these problems are solved by replacing the hammer and the right sear, but I'm too broke to spend the money and not exactly excited about having to dive back into the inner workings of the auto-glock hammer assembly (which I think I already mentioned, is an absolute fucking nightmare in my opinion).
I'm considering trying to bend the part of the trigger bar the contacts the sear. Just a little bit upwards and to the inside of the gun, so that it will make contact with the part of the sear that is less worn, and hopefully be able to stay latched when firing shots.