[roboticjunky]

Flexplate

The 6.0-liter Vortec with a 4l80E transmission is the only Gen III/ IV engine that accepts an early GM transmission without a flexplat adapter or spacer. These vehicles came with the GM spacer and bolts and the flat factory flexplate. These are basically the same components needed for the older transmission swap, just performed at the factory.

General Motors offers the spacer plate and longer bolts over-the-counter. TCI has conversion flexplates for automatic transmissions and kits that include the spacer and longer bolts. You must use a crankshaft spacer, such as the Hughes Performance, TCI, or GM spacer and bolts, or a custom converter must be made with a longer-crank hub. The Bowtie Overdrives LS swap torqueconverter eliminates the need to use a spacer; it bolts directly to the stock flexplate. If you’re installing a used engine, the best solution for the transmission fit issues is to use the transmission that came with the engine. Then all you have to do is fit the transmission to the car.

https://www.cartechbooks.com/techtip...-clutch-guide/