Lib /x64/ndpx64.fth (64 bit NDP)
Lib/x64/FPSSE64S (64 bit SSE)
Changing FPCELL is not a good idea. Writing words to convert 80 or 64 bit IEEE to and from 32 bit IEEE would be a better solution.
The VALUE FPSYSTEM tells you which FP package is the mail one. 2 for NDP, 4 for SSE.