My 73 340 did not have a bracket under the r/h rear seat, only the left. Basically the r/h came out of the muffler, up and over the diff, there is a rubber mounted pipe bracket that bolted to the shock cross member that supported the pipe, it then when down into the resonator, the back end of the resonator has a bracket that bolts to a rubber chassis mount to support. The l/h pipe comes out of the muffler, is supported by a bracket under the l/h rear seat, then goes over the diff into the resonator, then again, the back of the resonator has a bracket that bolts to a chassis bracket.