The stock Ford flat head v8 flywheel can be bolted to the crankshaft of the Ford flat head six and will work if the starter drive gear is changed to the 10 tooth v8 gear. The stock v8 flywheel physically bolts on the 6 crank shaft, clears everything and both are zero balanced. The stock weights are within 1 pound of each other at about 34 or 35 pounds, but the 6 has more of the weight concentrated around the outside of the flywheel, it is thicker in the ring gear area and thinner in the clutch area. The ring gears are different inside diameters so do not interchange between flywheels. The 6 ring gear has 114 teeth and the v8 has 112 teeth. The 6 starter drive has 9 teeth and the v8 has 10 teeth and are interchangeable. The starters are otherwise identical. There is another post some place in this topic where the poster wrote that he used a v8 flywheel and the matching 10 tooth starter gear and it worked. If I recall, the aluminum flywheels weigh about 8 to 10 pounds. The measurement from the front of the starter mounting plate to the back of the ring gear where the starter gear engages is .100 more on the on the 8 than the 6 but the starter gear in the unengaged position still clears with about 1/4 inch clearance. Therefore, the stock v8 starter with the 10 tooth gear will mount in the stock 6 cylinder location an will mesh perfectlly with the 112 tooth v8 flywheel mounted to the 6 cylinder crankshaft. A stock size v8 aluminum flywheel with the v8 ring gear will fit the 6 and work with the v8 10 tooth starter gear. After market gear reduction starters may work also but they engage the starter gear from the front of the ring gear, not the rear like the stock starter and should be checked for proper mesh, but should work. Don't forget to use the stock sheet metal plate between the flywheel bolts and the aluminum flywheel so that the bolts do not dig into the aluminum.
