• If using tall EV1/Bosch style injectors on LS7 or LT applications, there may be interference on low hood applications as on Corvette and similar. • 1999-2004 applications utilizing a factory supply and return fuel line will require the addition of a fuel pressure regulator when installing MSD fuel rails. • P/N 534-211 - Adapter kit, required when directly connecting Atomic fuel rails to GM factory fuel line quick-connect. Includes (1) 3/4-16 O-ring port plug and (1) -6 to GM quick connect adapter. • SPECIAL TOOL REQUIRED: GM 3/8" Quick-Connect Release Tool to disconnect the factory fuel line (these are inexpensive and available at the local auto parts store). • Fuel rails are machined to accept large -8 (3/4 -16) O-ring fittings (sold separately) - Earl's P/N AT985008ERL - 4 required.