Yeah..Add multithreading would not be that big of an issue and as for memory adressing its simply changing the header of the .exe and it will use up to 3.1 GB of RAM...thats the maximum as 32 bit app can do but anyway enough for any game on the market for the next couple of years.
Add new shaders and all that new stuff...Dx11 and all that...then add the naval battles pieces of code and voila...