Soak the airbox bolts two or three times within an hour or so with "plusgas" before even contemplating removing it..... Try one bolt after that 10mm IIRC... If it comes out OK then try the other two.... assuming all goes fine and they can be removed without shearing them off. Then any air filter will do just just fine... FRAM do a good standard filter replacement at the fraction of the cost from Alfa dealers....
A 1.8 is not really going to see much benefit from a performance variant so save your money on that side.
Assuming all goes well, (the lid comes off ok, the rubber sealing ring is in good condition and intact)..... etc...
1. Give the rubber "o" ring a very light smear of silicon lubricant to help it seal properly and keep it in tip top condition....
2. Vacuum inside the airbox thouroughly once the old filter is out... Saves contamination of the MAF with disturbed debris!
3. Give the airbox lid bolts a good smear of copper grease
to prevent and further issues of siezing
4. Refit the new air filter correctly making sure it is centralised and refit it all back together in reverse...... Job done
If all else fails and it goes pear shaped "which invariably it does" All is not lost... Get a cone filter kit instead and attach to existing induction pipe, place the filter inside the top of the airbox so you can protect it from heatsoak etc.... lesson learned.. Don't bother with cleaning it for at least 36,000 miles, just buy a replacement instead .
(same cost of repacing an OE filter over the same period of time) BTW
PS. Dont expect an Alfa dealer to take the care and attention described above in changing an air filter, they usually dont bother for that very reason