Up for Auction is a NOS GM New In The Box 8" Harmonic aka Torsional Balancer! These were used on COPO YENKO L88 ZL1 Type of Cars! The GM Part number is 3879623. This fits 1967-1969 Corvette ZL1 & L88 as well as Nova Chevelle Camaro SS COPO and Yenko. 396 L78, 402 375 HP, and 427 435 HP Engines. Don't chance using an old used balancer as more often than not they are not longer effective and the internal rubber has degraded! Replace it with this Genuine NOS GM Balancer! Check out my other items! Good luck and happy Bidding!