The 400SF is a converted passenger aircraft into cargo configuration.
I was a 747-200 pilot. We had same recommendation for ballast in a 200SF.
Located in CTR WING tank... to bring the CG forward...
Your empty CG is generally close to the main gear.
The center wing tank is quite a bit forward of the gear.
And in addition, in the 400, you got a tail tank too...!
xxx
In the 200 (like 400), fuel in main wing tanks would get CG to move rearward.
Empty, these airplanes are quite a bit tail heavy.
It is not as much the case in "real freighters". So they do not require ballast.
xxx
And on PAX airplanes, I asked to load bags 60% FWD, 40% AFT.
And fuel burn sequence, mains, reserves, center, is predicated for CG in limits.
xxx
Happy contrails