hi how r u? im in the process of doing the same on my 1986 560 sel. on ur 91 you shouldnt need the up grade part for the air flow boot. might check to be sure. i would think about replacing the thottle switch also. the rubber elbows on everything if u dont have them already. i got the clear tubing from ********a. dont forget the rubber mounts, all mine came apart. try to stick with factory rubber if possible. some aftermarket rubber is alittle flimsly and give you problems later. i had about 3/4 of an inch of oil. bugs, leaves, plastic parts, under my intake. it's a wonder mine didnt burst into flames lolol. to be sure i replaced eveything i could to insure longlong enjoyment of the car.