From my research over this several times is the aftermarket Ls Old school style flywheel is needed then you can use any clutch kit that fits your arrangement
I have seen a few threads where guys use the Ls Flywheel with 80s clutch pack the issue there is it only has 80 % contact face to the clutch
here is novaks page showing clutch face differences
https://www.novak-adapt.com/knowledge/gm-crank-spacing