These new crossmembers have been redesigned and are less expensive than the previous crossmember & work with engine mounting brackets BHS540 for both the GM LS & Gen-V LT engines. Choose the crossmember based on the transmissions that you want to run in your 1973-1987 C10: • Crossmember BHS548 fits 4L60E, 4L65E, 4L70E, 4L75E, 6L80E, 8L90E, & 10L80E Transmissions • Crossmember BHS549 fits 4L80E, and 4L85E Transmissions • Crossmember BHS550 fits T56, and T56 Magnum Transmissions These crossmembers, when used with BHS540, provide the ideal u-joint angles and the best clearance for 3.00" dual exhaust.