How do I make Xamarin on MacOS work with F # 64-bit?

I am running Xamarin 6.3 on macOS Sierra 10.12.4 It looks like when Xamarin is installed somehow from the .dmg downloaded from the Xamarin site only the mono-32-bit version is installed.

I am trying to follow these instructions.

So far mono64 has been successfully installed on my computer and in the terminal window I can do FSI in 64 bits

However on Xamarin after switching my settings here

(fsharpi64 is a modified script:

#!/bin/sh
EXEC="exec "

if test x"$1" = x--debug; then
   DEBUG=--debug
   shift
fi

if test x"$1" = x--gdb; then
   shift
   EXEC="gdb --eval-command=run --args "
fi

if test x"$1" = x--valgrind; then
  shift
  EXEC="valgrind $VALGRIND_OPTIONS"
fi

# Beware this line must match the regular expression " (\/.*)\/fsi\.exe" when fsi.exe is fsi.exe.
# That because the FSharp MonoDevelop addin looks inside the text of this script to determine the installation
# location of the default FSharp install in order to find the FSharp compiler binaries (see
# fsharpbinding/MonoDevelop.FSharpBinding/Services/CompilerLocationUtils.fs). That a pretty unfortunate
# way of finding those binaries. And really should be changed.
$EXEC /Library/Frameworks/Mono.framework/Versions/4.8.1/bin/mono64 $DEBUG $MONO_OPTIONS /Library/Frameworks/Mono.framework/Versions/4.8.1/lib/mono/fsharp/fsi.exe --exename:$(basename "$0") "$@"

      

        
        
        
      

    

)

I am still in 32 bit execution in Xamarin

The next unanswered question is how COMPILE in 64 bit in Xamarin