Just to close the loop, for other readers who may encounter this issue, the simple resolution was to:
1) Copy -all- .DBF, .FPT and .CDX files to another directory on your PC. Make sure you've exited out of both BigOven and Cook'n.
2) Run the Cook'n Import Wizard, which you can always find via Help/Import/from Cook'n. (It's a separate tool to keep download size smaller for other users.)
3) Point it to the RC*.DBF file, typically named RC65.DBF, and click Next
4) The import wizard completes, and writes out an intermediate file. It then calls BigOven, which loads that file into a new recipe box that you name.
That's it. Happy Cooking!