I know MoI is not intended as a conversion tool but it's SO good at it :)

I don't know if it would be possible to update just the polygon output module to 64bit as I don't think the rest really needs it as much. I use MoI to convert Inventor files (as well as model of course) and it runs out of RAM even on what would be considered relatively simple stuff by today's standards. No repeated patterns, instances, threads, or other fine detail stuff that would make it unnecessarily heavy. Just the basic critical structure, so there isn't an easy way of reducing the model size other than breaking it into more and more parts which is tedious.

MoI is such a useful tool in this regard I continue to use it even with the memory limitations.

Best of luck finding a solution that is practical. Cheers! - Len