Pre-68 engines [425, 330] had a different bolt pattern for the flywheel to crank attachment that the 1968 and up 350/455/etc. engines. So be sure you get a flexplate or flywheel with your engine.
However, there is NO difference between big and little block flexplates or flywheels. The bolt patterns are different for early [pre-68] and late [1968 and up] cranks, but the flexplates' weights' size and location are exactly the same for all. Rumor has it that Diesels used a thicker metal for the flexplate, thus making then heavy duty. Wouldn't doubt it. Swap to your heart's content.
OK, so we all know that these flywheels come in two flavors- early [pre-68] and late [68-up]. With the bolt pattern attaching it to the crank being different. The difference is something like the early one has one hole offset 5 degrees CCW and the later version has that hole, and another, offset 5 degrees *CW*. Why, you have got to wonder. So, I was comparing two flexplates [the AT kind] one day, and it looks to me like the weight is exactly the same chunk o' metal.
From a Toronado standpoint, all flywheels are the same from '68 to '79. Starting in '79, the Toronado, Riviera, Eldorado flywheels are a slightly smaller diameter. The rear drive cars are the same as the '68 and newer cars but are stamped "METRIC" and have additional converter holes to accommodate the newer style converters used on TH-200's beginning in 1979. They will work just fine in the older models.
http://www.oldsperformanceproducts.com/products.asp?menulevel=Flexplates/Flywheels
