Oddly the 4049UB and 4050B are listed on the same datasheet. 4049 is a logical inverter, 4050 is non-inverting. My understanding is the 4050 is buffered as there is another gain stage in each of the six sections, making it “buffered”. The 4049 inverter comes in both a 4049UB and a 4049B version, unbuffered and buffered respectively.
The 4049UB and 4069UB are useful for pedals and analog amplification, as their internal gain is small enough that they can be biased into the linear range. The B series inverters have so much gain that they’re effectively impossible to get to amplify as everything comes out as square waves, and they can’t easily be biased to give amplification although we would never discourage you to try. We cannot support a build however that does not use the correct components so if there is a support issue please try the proper chip.