A support and guide structure for at least one closed-loop conveyor with articulated links (M), wherein said links (M) comprise a first substantially flat portion , configured for the product being transported to lie on, and a second portion of mutual articulation of the links (M), the support and guide structure comprising: - at least one upper guiding element adapted to support and guide at least one conveyor in a forward path; and - at least one lower guiding element adapted to support and guide said at least one conveyor in a return path, wherein said lower guiding element comprises: - at least one first channel configured for at least partially housing the second articulation portions of the links (M) of said at least one conveyor in its return path; and - at least one second channel , developing in communication with and below a respective first channel and configured for at least partially supporting and guiding the first substantially flat portions of the links (M) of said at least one conveyor in its return path, wherein said first channel is delimited by an upper surface and by at least two side walls extending downwards from said upper surface , wherein said second channel has a cross-sectional dimension (L2) which is greater than the corresponding cross-sectional dimension (L1) of the first channel , wherein said second channel is at least partially delimited by at least one portion of said two side walls , wherein the support and guide structure comprises at least one plate removably constrained on the lower side to said lower guiding element , in particular to an extremal portion of said at least two side walls , wherein said second channel is delimited by at least one extremal section (32A, 32B; 34A; 36A, 36B) of said at least two side walls and by said at least one plate , and wherein said at least one plate reversibly closes on the lower side said second channel so as to form a sliding and removable support of said at least one conveyor in its return path, wherein the removable plate is provided with a first flat face and with a second flat face , said second flat face being opposite and parallel to said first flat face , the support and guide structure being characterized in that said second flat face has at least two spacing steps which are configured for abutting against the ends of at least two of said side walls and which are shaped and sized so as to increase the distance (H4) between said second flat face and the extremal section of said side walls , so as to also increase the height (H3) of said second channel compared to the situation wherein the plate is constrained with its first flat face in contact with the extremal section of said side walls , wherein the spacing steps are provided and develop at least at longitudinal extremal edges of said second flat face . - at least one upper guiding element adapted to support and guide at least one conveyor in a forward path; and - at least one lower guiding element adapted to support and guide said at least one conveyor in a return path, - at least one first channel configured for at least partially housing the second articulation portions of the links (M) of said at least one conveyor in its return path; and - at least one second channel , developing in communication with and below a respective first channel and configured for at least partially supporting and guiding the first substantially flat portions of the links (M) of said at least one conveyor in its return path, <EOS>