Michael
Thanks,Those hiding problems were not related to something being hiden at the time of saving, and the faces not displaying were identical copies of others which did display properly.
Verry odd. (And I was able to repeat the problem, in another working file, with both iges and 3dm but, in all tries, obj was fine.) See next.

Steve,
Both those settings for LWO and 3DS came up beautifully in Carrara. The LWO size was 11.4mb and the 3ds 9.32mb
Either, with those settings, will be my choice from now on.
Great! Thanks
Brian