I'm going to say the spring in the No. 1938 will be close or same as the Daisy spring used so commonly before the guns went to China: 21 coils, 7.5” free length, 0.082” wire diameter and unground ends. This spring must have been outsourced from various vendors over the years because they vary a little in almost every way (might have one or two more/less coils, ID/OD slightly different, differing free lengths, wire diameter could vary by a thousandth, etc.), but the spring rate stayed constant. And you're spot on about the new RR spring being a good part- ground closed ends, thicker wire, more spring rate, just a good overall spring. I just wish it was made with 0.095" wire.
One thing to remember about stroke length- the position of the air tube on the "over stroke" is important to the repeater function. The over stroke is when the lever has actually passed the point where the trigger would catch the sear, allowing the gun to shoot. The over stroke is important because it's where the AT has been pulled past the feed port in the shot tube allowing a BB to feed. Depending on how the stroke is increased this may or may not matter, but it's something that's easily overlooked so I thought I'd mention it.