I just checked the 60-no-dash I've carried for 40 years, and there should be some resistance when you first start to press the cylinder open. The locking bolt, which is that little plunger captured in the lug under the barrel, is under considerable spring tension, or should be. It has a bevel on the left side to let the end of the extractor rod push it forward easily when you close the cylinder. When you open the cylinder, the pin on the end of the bolt at the back of the gun pushes the center pin through the extractor rod and it, in turn, pushes the locking bolt forward to clear the end of the extractor rod, releasing the assembly to pivot out. The right side of the locking bolt, which has a relatively sharp angle, will ride across the slight groove between the extractor rod and the center pin, and you should feel that. It's a distinct break on my Mod 60. It's much less pronounced on my N-frames, probably because the sheer mass of the cylinder masks it, but it's there. My K-frames vary. My point is that the cylinder doesn't, and shouldn't, just flop open on any of them. You should feel a distinct click as it opens. If you don't, you've got a problem, anything from a binding problem that's keeping the locking bolt from doing its job properly to an over-long center pin.
If you're really having to push hard to get the cylinder to release, that's something different and we need to find the cause. The last S&Ws that used a right-hand thread on the extractor rod, to my knowledge, were the four-screw models from the late 50s-early 60s, and the Model 60 didn't hit the shelves until well after that. The left-hand thread was adopted so that the inherent drag on rod would tighten it rather than loosen it, so that's unlikely to be the problem unless you actually removed the rod from the extractor assembly. You didn't do that, so we can cross that off.
I believe you said you've already checked for grunge, loose brush bristles, etc., under the extractor star, so we'll cross that off, too. Does the crane move smoothly across its arc once the latch is disengaged? If not, take out the front screw and see if it moves properly. If that cures the problem, most likely you did mix up those two dome-headed screws and swapping them back will fix the problem. If it binds with the screw out, remove the crane & cylinder and look for some foreign material in the hole in the frame. I'd flush it with some sort of spray cleaner, wipe it out with an appropriate size jag and patch on a short rod, re-lube it and try again.
If the crane moves smoothly and it's just something interfering with the latch releasing, look for the issues some other members mentioned, like a loose thumb latch nut (it's a nut, not a screw) or foreign objects in the groove the thumb latch slides in or inside the lockwork between the bolt and the back of the recoil shield. If none of this solves the problem, it's time to consult a qualified pistolsmith.