The v5.41 versions should be up for all 64 bit systems. The manual details the changes to the floating point and the callback mechanisms. The default FP pack is the NDP387, and if you want to change it, the incantation is
remove-FP-pack
include %lib%/x64/Hfpx64.fth
or
include %lib%/x64/FPSSE64S.fth