Odd OMC Model Number I Cannot Completely Identify

[SSG_Clapp]

I have an OMC 5.0L in a 1987 Bayliner and would like to know what the last few digits in the model number mean. I have looked on several websites and manuals and cannot find my model number so I can identify exactly what I have. Can anyone help me identify this model:504APWX. I know that the 50 stands for a 5 liter engine and the 4 indicates a 4BBL carburetor but am not sure about the rest because it is unlike what I have seen online and in my aftermarket manual that I have. Thanks much!

 

[bilge rat jim]

A indicates this is a "first" model run, P is for power steering, and the WX is the model year code- 1986.