YamahaMark

Just got a 1990 FZR600. Its fouling the spark plugs badly and uniformly across all four plugs. The NGK web site says it should have non-resistor plugs. The plugs that are in it are resistor plugs. The NGK web site shows Yamaha using resistor plugs only after about 1995 or 1996. It has a salvage title. I'm wondering if someone put a later engine or at least head in the bike that takes smaller plugs (10mm) rather than the 12mm plugs that are spec'd.