Performance Header Gaskets Fits 1968-1992 Chrysler 318/340/360 4-Barrel LA Small Block Mr GasketMr. Gasket Performance Exhaust Gaskets are manufactured from high temperature composite material. They provides maximum torque retention to eliminate Gasket failure. Precision die cut for an excellent fit, but can be trimmed if necessary for modified port applications. For OE replacement, high performance street, drag race and oval track. Rectangular Ports, 1. 30 inch x 1. 8 Inch inch Manufactured from high temperature acrylic blend exhaust material