I've attached a 64-bit version making only some small changes to the original 32-bit version to show how easy it is to do. For instance, the structures make heavy use of the ptrdiff_t typedef. This allows the size of the structures to automatically grow when pointers are field members.
Notice how similar this code is when compared to the original 32-bit version. With the exception of the use of 64-bit registers in certain required locations the majority of the source is unchanged. Note that this example is not the best way to use the new Win64 calling convention. However, it does show how easy it is when using NASMX.
Note that the windemos.inc file was modified ( again! ) to include some of the new functions I used for program cleanup such as the addition of WM_CLOSE handling and a change to VKEY processing. Together, they make for tidy program cleanup.
Edit: Spelling.