The GM #3991428 clutch friction disc was used only for 1971-72 ZR-1. It is exactly the same piece as the GM #3886059 used for 67-69 L-88/ZL-1 and 1970 ZR-1 EXCEPT it has a 26 spline hub versus the 10 spline used for the earlier part.
This piece is NOT for sale.
This piece is NOT for sale.