hi ruzfactor,
As a quick check I have built your circuit using the LM324 and 74LS151.
Used a number of different LM324 and 74LS151 ic's.
Highest values at the output of the LM324, +0.65V low and 3.7V high.
If you add a 2K2 pulldown resistor on the outputs of the LM324 you will get
a low of +0.5V and a high of 3.6V, which is good enough to drive the LS151
If you cannot get the LM393, try the LM324 it will be much better than the 741.
I would strongly recommend that you try to source a LM393 as it will give a more reliable operation of the circuit.