Well here is what NGK sez:"I don't care what the cross-reference books say is correct plugs for 164 12v V6 engines they are usually wrong."
Just went to Amazon for the BPR7EIX (4055) and sure enough, they say does not fit my 164L.
1991 ALFA ROMEO 164 3.0 V6 FI L-MODEL
Spark Plug Part No. Stock No. Plug Gap Photo
Standard BPR7ES 5534 .025
Iridium IX BPR7EIX 4055 .025