78L05 as LM2931 replacement for powering 4XXX logic?
As a regulator yes, it should give you the correct output. Some manufacturers datasheets suggest a 100 nF output capacitor on a 78L05 too.

Be aware though, you're dropping 7 V, the TO92 78L05 can't handle much power dissipation, so depending on your current draw you might want to step up to a TO220 part.