LSX Magazine wrote an informative article on installing an older non electric transmission to your LS based engine. The basis of this type of swap lies within the flexplate and a spacer. Take a look at the in depth article here:
Video Above: PRW Part # 1834624 GM LS High Inertia SFI Rated Flexplate which fits all specialty torque converters.
This is a great article that will answer the many questions about this popular swap. Thanks for the info LSX Magazine!