Is this possible on an SAFC2? the only way I know it does it is with senor IN and OUT settings, but at that point how would you determine the IN point, cuz i'm sure the out has to be the same as the ECU.

ex. (these I know for sure are correct)
RB20DET... running z32 n60 maf... IN 2, OUT 4. draw thru setup
RB20DET... running r32 oem maf... IN 4, OUT 4. draw thru setup


this is what I'm trying to determine:
RB20DET... running r32 oem maf... IN 4, OUT 4? blow thru setup
RB20DET... running z32 n60 maf... IN 2, OUT 4? blow thru setup

BUT because there is piping in the mix for a blow thru setup (2 and 2.5in piping) and the maf is a 3in diameter, the reducers will affect flow readings and I'm sure the smaller diameter piping also affects flow readings compared to a draw through setup.

I hear voltage readings can be up to a +/-1v off. Example being draw through setup reading 3v in but blow through setup in same situation reading 3.9v.

How can I determine and compensate for this reaction?

This is something that you'll have tune once you get it up and running. Set the in and out for your engine vs. mafs and then tune from there. If it's WAY off, then you can mess with the in and out, but I've never had to do that honestly.