The threaded hose would be correct for a 3200/3600. I ran into the same problem, as the correct 3200/3600 hoses are not available. On the 3100, the hose, in addition to being longer, is attached differently. The 3100 has the criclip on the outside that you mention. There is also a U shaped spring clip, similar to what holds the parking brake cable in place and what most modern cars use, to retain it in the frame. The clips are not included with the hoses.
I've been running 3100 style hoses, installed with the spring clips, on my 3200 since '94 with no problems. I do understand your frustration, I went through the same thing with mine. Seems most parts stores don't realize that just because the 3100 and 3200 are both 1/2 tons, they aren't necessarily the same under the body. The 3200 is really more of a light 3/4 ton than a 1/2 ton.
Yeah it's weird. I just got the correct hose by letting Napa match them up. The length and fittings seem correct. I'm going to try it. I have one on the pass. side that's older USA Napa made probably in the 80's and it was a perfect match. They switched over to the circlip BS to save money IMO.
It's easier to make then a internal/external threaded end.
