Rear of 91-93 164L single outlet cat connection uses copper gasket between two fixed three bolt flanges welded on cat rear pipe and front pipe of center muffler. Rear flange of center muffler and front flange of rear muffler at 164 models uses two floating three bolt flanges with steel sealing donut between the 45 degree flared ends of those pipes.
The 164S cat has dual outlet pipes and mid-muffler has dual inlet pipes. One side has fixed welded flanges with gasket and the other pipe has sliding flange with smaller sealing ring on cat pipe and fixed flange on mid muffler inlet pipe.
The 24v Q/LS mid muffler front pipe outlet and cat rear outlet have floating flanges with steel sealing donut in between like rear of center muffler and inlet of rear muffler. I know this because I had vender ship me 24v mid-muffler for my L one time and had to send it back and get correct mid-muffler for my 164L.