Finding Values from one Column and replacing equivalent row in seperate column

[m.raby]

Here is the setup:

In Column A, I have a list of thousands of part numbers which each have a specific part number.
In Column C, I have a column which I desire to be filled with military part numbers (This is not specifically populated yet for all entries in Column A).

In Column Z, I have a specifically filtered down list of a few hundred part numbers. These part numbers all match a part number in Column A (But these are not in equivalent rows).
In Column AC, I have the specific filtered down military part numbers that are associated with the part numbers in equivalent rows in Column Z.

What I desire to do is Find part numbers from Column Z, search for them in Column A. When it comes across the same part number in Column A, I want it to replace the same row of Column C with the same row that it matched up with from Column Z in Column AC.

Ex.

What I have now:
Row# Column A Column C Column Z Column AC
25 100-10-8 (blank) 111-10-8 M25/12
50 111-10-8 (blank)

And I desire:
Row# Column A Column C Column Z Column AC
25 100-10-8 (blank) 111-10-8 M25/12
50 111-10-8 M25/12

This is the case for several hundred part numbers, which would be annoying to find and replace them all.

Any assistance is appreciated.
Thank you,
Marc