The File "Ldr.bin" I think is correct:
1. I downloaded from your Navigator to a file called "GUPDATE.GCD" from the folder "system"
opened its programme RGN Tool
saved as "boot.bin"
renamed "Ldr.bin"
2. Created file "Update.txt"
rrgn,154,2:/154.bin
reboot
3. On the memory card created a folder "Garmin" --- "Updater" --- "1948" and copied there the "Ldr.bin" and "Update.txt"