I highly recomend oxygensensors.com if you need an oxygen sensor, the local dodge Dealer wanted $119 and didnt have it in stock, $atan wanted $149, and the local Autozone, Pepboys etc.. wanted about $99 for a universal that you have to splice in. I ordered from oxygensensors.com and got Denso OE that pluged right in for $49.99 + shipping and it arrived in 2 days. Mine was for a 4G63, but they have great prices on the 420a ones too.

99 GSX: 16g, Injen Intake, Greddy FMIC, RRE Down pipe, RRE UICP & LICP,
3" Test Pipe, 3" Apexi Cat Back, Greddy Type S BOV, Greddy Profec B,
Fluidyne Radiator, K&N Air Filter. Walbro 190 Rewired, Eibach Prokits, Tokico Illuminas.
ARP Head Studs, Adjustable Cam Gears, Energy Motor Mounts, B&M Shifter + Symborski Kit, DSMLinkl

Parts Not Installed Yet : EVO VIII 560cc Injectors, Fidanza Flywheel, XTD Stage 3 Clutch

i concur.