Can you state the part number of the RAM chips you used?
What do you mean by "using 1 rank" ?
you probably would need to modify the EDK UEFI
My 2 cents,
What amazes me most is that you were able to get the BGAs removed and new BGAs soldered without damaging the board. Thats pretty awesome...
But yes, sounds like you need to take a look at how the UEFI detects and registers the available amount of ram for Linux to discover.