The late war AC-45 K-43 represent the breed perfected, and are among the most desirable, IMHO. There are characteristics of late war AC-45s that are not seen in rifles from other manufacturers. These represent distinct product improvements, not just random changes.
The dual bolt lugs give better support to the bolt, increasing reliability, which is not a strong suit of earlier designs. The extractor has been re-positioned on the redesigned bolt. There's a small added cross pin in the rear part of the receiver that prevents sear binding. The gas piston is made of stainless steel, and the gas cylinder has added three millimeter holes that prevent the cracks in the rear of the receiver common to earlier guns with their violent operating action. The recoil lug has been moved well forward, for added strength (stocks from earlier guns will not fit late AC-45s).
My own c block AC-45 K-43 has shown itself to be absolutely reliable. There's been no need to install a "shooter's kit", or even after market springs. Instead of the violent action of earlier guns, the bolt cycles smoothly and gently, almost as an after thought. There's little damage to fired brass. The rifle is very accurate, and has the original adjustable trigger. Trigger take up is long, but the break is light and crisp, with no creep. Late AC-45s used product improved Zf-4 scopes, most made by Voightlander (ddx). Zero is not disturbed when the scope and mount are removed from the rifle.
Metal parts on late AC-45 K-43s can be a mixture of blue and phosphate, or all blue, or all phosphate. That was just luck of the draw during assembly. On the back of the receiver below the safety lever there'll be a marking, most often a heart. No one seems to know what this signified.
Darrin Weaver says that the dual lug was removed from earlier guns because it caused problems and was simply milled off after initial forging and milling. (Yes, all G/K-43 receivers are forged, and not cast). If this is true, why did Walther start producing dual lug guns, and go to all of the trouble to redesign the bolt?
FWIW