You cannot mix and match just the input shafts. The bearings on the midplate that the input shafts ride on are different sizes. They’re very close visually, but the LT1 shaft is about an 1/8 inch thinner in diameter than an LS. The LS bearing is also a bit thicker than the LT1. Even though both are 31 tooth gears. You have to match the input to the midplate. you cannot put the LS input in the LT1 midplate. And you cannot put the LT input in the LS midplate. Not and have the bearings be correct or with issues with the bearing retainers as well as the play on the shaft. You’re gonna do more damage trying to hodge podge it.
Yes, you can convert an LT1 t56 to have an LS1 input shaft or even a viper input(assuming you also upgrade the counter shaft and main shaft) but you have to use the corresponding midplate . Unless you do some custom matching
Furthermore you have to make darn sure the LT1 t56 is a 31 tooth t56. Some, mostly 1993s and early 1994s were 29 tooth and youd have swap the entire gear set to swap it. As well as the main and counter shafts. And that’s expensively done.
You also have to watch the spline counts between some of the Fords. Most shared the 26 spline inputs but some, especially those in gt500s in certain years contained a 27 spline, 31 tooth input.
Corvette t56 t56s are an entirely different animal with their built in transaxle and stupidly long out put.