Is there a way to tell from the header of the exe which version it was created in?
Yes and no - probably no with VFP executables as you'll just get references to the MS Visual C++ libs.
Try uploading your EXE into this: http://mark0.net/onlinetrid.aspx
Or download TrID from that site and try it locally. You could also use Dependency Walker but on testing here it again just lists all the Windows DLLs that the EXE imports.
http://www.dependencywalker.com/