In North America, issues of monthly magazines tend to be off by one or more months. See here for reference:
https://en.wikipedia.org/wiki/Cover_date
In the case of American Rifleman, the April issue was delivered at the beginning of March. As such, the Klein's ad shows the status of Klein's inventory for March, 1963. Anyone who ordered C20-T750 in March was ordering a 40" long rifle.
As such, the Klein's ad shows the status of Klein's inventory for March, 1963. No it doesn't. At best it shows what they were offering for the month of April 1963.
The February issue showed what they were offering at that time and that's the rifle that was allegedly ordered by Hidell.
Anyone who ordered C20-T750 in March was ordering a 40" long rifle.Where in the February ad for a 36" rifle does it say that rifles ordered in March would be filled by 40" rifles on offer in April?
Silly, right? Well, that's how idiotic your argument is!