Tru Power Engine Kit. 6-Cylinder Gas, 291 CID. 3-3/4 inch Standard Bore. Contour Step-Head Pistons. Basic Engine Kit, less bearings. Contains sleeves & sleeve seals, pistons & rings, pins & retainers, pin bushings, complete gasket set, crankshaft seal. For 2706 Series, 2756 Series, 666 Series, 686 Series, 706 Series, 756 Series, 766 Series, Hydro 70 Series, Hydro 86 Series.