I have no hands on lt1 experience, but it may be possible for the lt1 flywheel to fit your setup, since the lt1 is pretty similar to later gen1 blocks. You'd need to do a little research to confirm this. (I went straight from gen1 to LS1). You'd be good to use most similar to what lt1 came with. Lots of different factors in clutch size ,materials & pressure plates specs .This all varies according to your planned use & needs You're most likely best to not worry about considering lighter flywheels at this point. Now you do need to worry about your rearend ratio. You can look up what 1st & 6th gear ratio your year t-56 came with (google).
You likely want something close to 3.42 gears, maybe even 3.73 for extra performance.