I was getting good answers here but the Mods whacked the post and responses. Geesh
As far as I can tell this request does not violate /r/hardware rules. Even rule #5. I wasn't looking for tech "support" but rather just asking for this communities guidance/experience on SD cards partition table and formatting.
To clarify: I have written my own "disk operating system" for an MCU. I simply reads and writes for the first 2Gb of an SD card. I need to write my target image to be loaded on to the MCU at 0x000 and I find that the MBR resides there. I have to load the image from a desk-top PC and the MDB and GPT put me way further into memory (0x01FF).