Typical GM bolt patterns are 10.750 for TH350 and 11.500 for TH400. The LS uses a 11.080. We have a SFI flexplate that has both the LS and TH350 holes. You also need to make sure the pilot is long enough to fit the crank. The LS cranks sit a little deeper and require a longer converter pilot. Typical GM pilot to pad is ~.200 and the LS is ~.500. So you might need an extension.....Hopefully this made sense.