As people have said, the MSXX bottom plate is the same as a MRE bottom plate, but thinner. You don't to change the centre shaft of pulleys at all. I am still running the original pulleys my MSX came with in its box, and there are no issues with using those parts on the MRE/MSXX. Sure the MSXX and MRE do run a different centre shaft setup, but the bulkheads have everything in the same location as it was right back to the original 415. My MSX front and rear aluminium bulkheads fit fine on the MRE plate, no need to modify holes or do any modification to the bulkheads.

You can go for the different pulleys and/or centre shaft, just depends on your budget. But it isn't necessary.