Definately zero flat grind for those as Rob say's, the best way to remove the metal will be on a coarse flat waterstone or if you have access to one a continuous grit diamond stone for swift perfectly flat metal removal, but not the standard DMT coloured stones with the holes revealling the plastic mount, they can leave a fluted effect on the grind and be careful not to run right into the rounded ricasso though with diamond stone, they have square corners and will swiftly mark a sharp angle where it was curved.
Personally I use the Continuous grit diamond stone for rapid flat removal staying 2mm away from the ricasso then use a slightly modified waterstone, in that I rounded the corners of with a cheap copy diamonstone thing I got in a set of 3 from Aldi years ago. The advantage of this way is once the grind is flat its easier to keep it that way on the much softer waterstone.
Another tip for keeping soft water stones flat without spending over £200 on a lapping plate is to use the coarse stone from Aldi, mine is bonded to a 4mm thick plastic base plate so is flexible thus no real good in the workshop(field emergency sharpening only) and glue it with expoxy to a piece of 8mm glass inturn glued to a bit of Ply.
Bit long winded but I hope it helps