If the speedo works, then the plastic gear is o.k. just the cable housing is bad, causing the cable within not to turn smoothly- maybe pull out the cable from the trans end, oil the cable or rub light grease on it and try it. There are plastic gears with all kinds of tooth counts that go with certain rear gear ratios to make speedo read right, so dont just go replacing it just because.
I guess if the steering box leaks a bunch, thats a good reason to switch out, especially to get the $100 bucks back.
The Pcv system will certainly keep the outside of the motor clean since no oil vapor will be settling all around the motor. I never heard the claim that it will keep the oil cleaner, it certainly cant make it dirtier. The more cylinder wear the motor has - the more "blowby" the engine will make. This is why the road draft tubes tend to make the outside of old motors so greasey. I once saw a '58 cheap body six from Calif. with a Calif mandated pcv system added to it. It had a pretty clean exterior. From your pictures your motor was either recently washed up nice or else it has very little "blowby" indicating a good tight motor (little cylinder wear)
The old filters were not of the full flow type, so a lot of the oil never passed thru it, so they did not do much for cleaning the oil-but It could be said that every little bit helps. A long time ago My dad and I went thru an 83,000 mile old '54 235 with no filter, but had a life time of regular non-detergent oil changes, and the bores went back std, and one rod bearing had just a half thousand journal wear and so all bearings also went back together with std size.
Old cars can hold up good, if they are cared for! Oh yeah, dont bother trying to find non detergent oil- detergent oil works fine. The detergent oil tends to keep the dirt in suspension, to help prevent sludge collections inside the motor- and do run a thermostat, (180 is good) let the motor run nice and warm, as this prevents moisture from condensation from contaminating the oil, and also contributing to the sludge buildup.
