Hi Sun, currently I don't have any plans for a 64-bit version of v3. It would take quite a lot of effort to make that happen, it involves not just MoI's core code but also getting 64-bit versions of various support libraries that MoI uses as well so altogether that's a highly time consuming project to undertake.

If you have a pretty complex model your best bet is to select some portions of it and use the File > Export command which only writes out just the selected objects instead of writing everything. Writing things out in a couple of chunks like that instead of all at once should help to avoid running out of memory.

- Michael