Filters arent really a complex thing.

Measure the space available to you, look at the shapes/sizes in the filter catalogue and order one that fits in the space.

https://www.knfilters.com/dimsearch/index/

Good that you pointed out the airfilter setup. I've done the math and found out that I should get a bigger one.

I will be testing pressure drop. I have a differential pressure gauge that seemed to work great to optimize ducting, so should work.

This is the setup:

Tube going into breather fitting, about 1 inch horizontal distance from the compressor inlet:
https://cimg1.ibsrv.net/gimg/www.mia...46986ae728.png

Tube Right at the air filter:
https://cimg6.ibsrv.net/gimg/www.mia...7771b2353d.png

Both tubes are the same length and run along the same path to the cabin.

Does this look decent?
Is the filter tube positioned correctly?