Paul, The plastic parts are the ones the original air inlet tubes attach to next to the fan housing and radiator. Congrats on the new mods. You will not be dissappointed. I did the 74mm & retune and I swear the car seems like it ran better with the 68mm & old tune. Good luck with the install. You shouldn't have any problems, everthing went together pretty easily. See you at the winery.