The 4050 when powered from 3.3V takes in 5V signals and outputs 3.3V signals.
"They have a modified input protection structure that enables these parts to be used as logic level translators which convert high-level logic to a low-level logic while operating off the low-level logic supply. For example, 15-V input pulse levels can be down-converted to 0-V to 5-V logic levels. The modified input protection structure protects the input from negative electrostatic discharge. These parts also can be used as simple buffers or inverters without level translation."
So, power from 3.3V as you seem to have done, and you should see 3.3V levels out.
Write a simple sketch to just drive the output pins you are using High and low for a couple seconds, you should be able to follow the outputs as 3.3V level signals with a multimeter.