These fellas were kind enough to give you the rough estimation for how much you'd end up with. But, just be sure you do separate transactions to convert your RSGP.
First: RS3 -> FG, then use the FG acquired for your OSRS gold. Straight RS3 -> OSRS is an Illegal Trade here.
You may have already been aware of this, but figured I'd post it here to be on the safe side.
Have fun 'scaping
