Nope, there should be 2, 7/16th nuts at the bottom of the transom that hold the manifold in-place, removing 'em allows pulling the manifold down, to unscrew the inside lines,....
Ayuh,...... Did yer motor have exhaust shutters,..??
If so, I've found that burnt up shutters in ole Mercs can fall down into the y-pipe, 'n rattle,.....