In case someone is interested, here are some photos I took a while ago. I had two Pentax-M 50mm f2.0 lenses, one with jammed focus. I tried to keep one mostly assembled as a guide for the broken one. It worked, and I got them fixed and back together.
In the first photo, the left lens just has the mount removed. The right lens has a lot of front disassembly already, the mount, aperture ring and silver ring that rests between the lenses removed. This silver ring has a notch that fits a key on the aperture ring, and a short round bar that should face towards the front of the lens. The short bar fits into the aperture control mechanism and keeps the aperture from opening wider than the aperture ring setting. This ring just lifts off. It doesn't really work or fit upside down. By the way, the aperture ring usually is holding in a small, spring loaded ball bearing that makes the lens click at all the stops. The bearing will try to shoot off into outer space and you'll never find it, unless you are prepared. Open the lens in a plastic bag, box or other controlled area, find the bearing and keep it safe.
The left lens now has the silver ring removed. The right lens has the aperture control mechanism removed and placed between the lenses. This has the lever that goes into the camera, a second lever that goes further into the lens to move the blades, and a return spring. Three screws hold it in. The lens on the right has a copper tab removed. These tabs connect the focusing helix to the lens. If you remove these and unscrew the helix, you might spend an hour getting the lens back together correctly.
Here is some front disassembly, just one lens this time. The "name ring" comes off first, and you'll see three screws. They hold a short barrel that has the filter threads. Remove that and on this lens you'll see more screws. The brass ring holds down the front lens group, which is upside down and to the right. You can't see the three screws still on the lens which attach the focus ring to the lens body. These can be removed but you'll need to adjust the lens for infinity focus upon reassembly.
Other Pentax lenses are similar, The front lens group is frequently mounted in a threaded carrier that screws in. Only the cheaper lenses use the brass ring. Older lenses have common screws instead of phillips, and brass instead of aluminum where the focus ring attaches.