Heptahydrated makes sense, in that I suspect it's half sulfite to H2O, so simply use twice as much as anhydrous. Probably preferable stock, too, if it's supposed to go into solution in water since the anhydrous will presumably degrade quicker. So not knowing whether I bought anhydrous or hydrous, I now have a 2X error margin. I guess I'll go back and get the Kodak anhydrous.
But... I did a search on photo.net, and found someone posted using 4g/l with Rodinal 1+75 -- that's 0.4%!!! Someone else agreed, but they used 5g/l! That's got to be a teaspoon or so. I hope they were simply mistyping, meaning 40 or 50g? I would have expected half a percent to have a nonexistent effect? Now I'm totally confused.