[WSSix]

1.75 works well for a wide range of motors being used in the swaps would be my guess. Don't forget, the 5.3 is used a lot in these swaps and that motor does not need 1.875 headers. 1.75 headers also work very well in built 6.0s. You may give some up over the 1.875 headers but not much. Combine that with the fact that the 1.875 headers are probably harder to package in the engine bay even thought it's only 1/8th more. Just a guess on my part really. I wouldn't worry about using 1.75 headers on anything smaller than a serious LS3 if that's all that was available.