Mark, you may also try Masa paper; works great with every iron / iron-silver processes I know. (Even Argyrotype!) Beware: It's a thin paper (something around 90 g/sqm), therefore, if you print large (> 11x14") you will have to be careful when handling; may tear and/or crease easily. (Don't be intimidated; it's much stronger than it sounds...) And, as a last note: Try Vandyke w/o citric acid first, use it only if it doesn't work otherwise.

Regards,
Loris.