The 0523 is both a compressor and a vacuum pump, depending how its plumbed? CORRECT you are.

The numbers at the end, IIRC, have to do with the extras that come with it. This is the one I bought,,,

Gast 0523-101Q-G588NDX Vacuum Compressor (Proprietary No. 0523-V191Q-G588DX)

You need to to include each line, there size, & lengths to sum up the line pressure losses. You only need to add in the deepest diffuser for it's head affect on the system and only one diffuser's worth of pressure requirement to operate. Then add the fitting reductions. This should give you a decent operating pressure so long as you assumed the correct operating CFM to begin with.

NOTE: I use the following online calculator to run the numbers...

https://www.engineeringtoolbox.com/pressure-drop-compressed-air-pipes-d_852.html

You have to guess where on the curve the pump will operate and use the CFM and pressure from that point on the curve, then run the calculator to get the pressure losses for each line, then sum in the head loss, fitting losses, diffuser losses and see if it closely matches your original pressure point guess. If it does not, average your initial guess and the calculated operating pressure, take that to the curve and get a new CFM, run all the calcs again. Usually within a few iterations of this you get the initial pressure to closely match the calc'd pressure and your done.

Hope this helped...I'm short on time today and have to get back to it.