Search for Argus Collectors Group. There are manuals and even military version service manual online.
The shutter cocking lever is threaded on, with 'jam nut' underneath. You can loosen it by turning it the wrong way, reposition the jam nut and tighten it wherever you want it - I suggest 180 or close to 180 degrees rotated. If you avoid getting a manual, you won't know what it's supposed to look like.
I don't think the shutter speeds are continuously variable like the aperture.
I also have three. One gave me two rolls of double exposures. I really can't believe it was my fault, but I did shoot two more that were fine. I can't comprehend I could actually do that.
Interesting variations. I have a C3 Matchmatic (EV numbers) and two C3's from early/mid 50's. They have at least 2 different shutters among the three. One has 7 speeds, and I think only 4 or 5 on the others. All have coated 50 mm f/3.5 lens but different barrel & thread. One used Series V filters and I think the older ones use Series IV - odd, considering the specs were the same for the lens.
One of my favorite photos came from the Matchmatic - go ahead, laugh.
I just smelled and focussed the two older ones - I just got them recently from a relocating person at work, and the rangefinder focus is a 'joy' to use on both (at least looking thru it; who knows if accurate).