Hi Mark,
OK - below is my HK Early S. It is a matched mag, and may rate at 96+ blue/65% straw (I grade tough, and sorry for the incandesent light reflection, but - this is an older photo).... It's a nice piece, but later then yours in serialization.
By comparision, the recoil lever in mine is blue and the hold open is not strawed. As yours, it also has the rather classic HK wood grips, which I really like. As well, my mainspring giude DOES have rough machine marks, as yours..... I'll take a look in my notes, but I believe HK serial number "41X" (sorry, it's not mine any longer, so I won't publish serial numbers of other's HKs) but, as I recall - it also had a strawed recoil lever? I'll check....
Anyway - here's mine - and I'll try to post some more pics when I have a chance to get the camera out do a quick write-up....
Again - my thanks for a great presentation of a fine Early S HK!!!