i have an lbz and had to change the rt up pipe due to cracks in the weld at the flanges no soot but sounded like a leaky exhaust manifold on an old 350
while you are there i would check the up pipe on the rt side looks like the flange weld cracked in side the flange on top. there shouldn't be any oil around where the up pipe meet the flange for the gasket.
no the piston is not included in the kit but before you rebuild it look at the piston seal on it a friend of mine had a similar issue and come to find out the piston seal was torn