Tony,
i wrote a program in C++ which converts MF idx-3, idx-4 or c-isam format to fujitsu cobol format. it can not deal with idx-8 format. it will need both MF runtime and fujitsu runtime.
i am unable to post the source here, because it is part of a system containing about a hundred of c++ sources. i want to send the executable to you if you want to post your e-mail address here.
if you want to go the way etom suggests, look in MF documentation for the callable file-handler, "EXTFH".
Marcel