RNDP 6350 will not start

An image of somebody else's flash will include their serial and model number information, so it's unlikely anyone will provide it.  If the MBR was corrupt, I don't think you'd get that far in the normal boot, and the USB recovery seems to be doing what it's supposed to.  The NAS does need to recognize the hardware via the DMI information as well as the model and serial number via a file in flash that USB recovery saves and restores, but cannot create if the original is corrupt.  I think it's Netgears effort to keep anyone from creating a "do it yourself ReadyNAS", and I think that is the likely source of your problem.  I have tried running the Readynas OS on generic hardware (the same motherboard as used in the RN4200V2, to see if replacement is a possibility) and got a similar response.

If you can put the unit in Tech Support mode, PM one of the Netgear mods the 5-digit code and a photo of your serial/model number label and see if they can fix it for you.  Otherwise, if you are in a hurry and the unit was not converted to OS6, you can engage paid support to do the same.