Engine should have same year of production or younger as car. Exhaust not louder than stock. It is recommended to use stock parts (if possible). Brakes should at least be equal to those used in the 325. ABS not especially needed. If your car is not a 325, you need a affirmation from bmw, that your brakes are equal to those from a 325. Strutbars front/rear Engine mountings should be made from St37-2 steel. Well constructed. Differential ratio can be freely chosen. Drive shaft must be balanced (keep voucher) Load index of tires should be watched. General Clues: Engine compartment should look good and proper. D'ont hassle withe the mountings. All weldings must be done good solid. Enough space: 1,75 inches to cooler/splashback. half an inch to axle/ oilpan Hood should be easily closeable. Expertises of all parts sheeted at the car. Sorry for my bad english, but I don't have the opportunity to write often...