Converting one chassis to another chassis by replacing backplane is not supported. You will face fitment issues. Chassis for 4X3.5 and 8X2.5 are completely different. The backplane and cable part number you mentioned are correct for 8X2.5 backplane. For cable you can use 7NKWC also.
Hello everyone I have a PE R430 with the 4x SAS 3.5inch backplane, connected to a PERC H730 mini (embedded) raid controller. I also have 2 Delta 550W PSU's.   Can I upgrade the backplane to the 8x 2.5inch version? From my research, the part number is MG81C, but it needs a different cable to connect to the raid controller, since it has 2 SAS connectors. The cable for that should be ND4YM.   The chassis does not look like it's a problem, but the backplane guides are in different places.   It's possible to upgrade from one backplane to another? Are the parts the right ones? If anything is wrong or you need more info about my system, let me know.   Thanks in advance!
Poweredge R430 upgrade/replace blackplane