The 1933 International Truck Model D1 used the 80 bhp engine intended for the side valve Willys 99, which in itself was developed by Willys from the 1930 - 1933 65 bhp Willys 6. Refer Page 12 of the Willys 99 Sales Brochure. When Willys sold the engine design to International, the same basic design was used on subsequent light truck models through to the late 1940's with very little change and was known as the "Green Diamond" engine. The "Green Diamond" cylinder head and connecting rods will fit 1930 - 1933 Willys 6, however the bore and stroke are different, so the pistons and crankshaft by themselves are not interchangeable. With some work to allow for the differences in front engine mounts, cooling system hose diameters, etc, the complete engine could, and has been used in a Willys 6 restoration project.