[edit] okay so i just realized which forum this was posted in (i use view new posts instead of browsing individual forums)... at least i now realize what 'LO' stands for in the above posts.. please ignore the following 😄
maybe i'm not understanding your problem correctly but i just tried -->
--open two windows - one set to decimal/mm and the other to architectural/inches..
--in the decimal window, draw a circle measuring 20,000mm diameter and group it..
--copy that group and paste it into the architectural window..
--measure the diameter which is ~65' - 7 3/8"
that's a correct conversion...
is this not what you're trying to do?