90 Lx 5.0 Rebuild

Ok, lets get a couple things cleared up
If you have a cai with a filter on it your good.
Don't put a filter in or on the maf.
You may have to turn the maf body, if your maf sensor is on top, thats the 12 oclock position, move the maf body so the sensor it at the 3 oclock position, that will change where to sensor is in relation to the air flow, this may help like mike says.
Don't worry about the screen that is in the stock maf body, you likely do not need it in an aftermarket maf
And yes, you need to clear the computer after upgrades, disconnect the negative battery cable and turn the headlights on for several minutes, this discharges the diodes, turn the headlights off reconnect the cable, start the car letting it run at idle for a few, it may hunt around for a couple minutes, take it for a drive running in some stop and go traffic and some time at steady speed like 50 mph or more for a time then check for codes.