Hi Ian, AFAIK, pure pt printing has problems with gelatin coated papers - the remaing criteria is the same for all iron / iron-silver processes. Therefore, despite I haven't tried it with pure pt, I'd like to suggest you trying sulfamic acid treated Fabriano Artistico Extra White paper. I've used this (treated) paper with the most finicky iron or iron-silver processes (new cyanotype, argyrotype - plus another easy-going process; pop pd) and it worked flawlessly with each of them! This paper has a strong AKD sizing, a very nice bright white (but still natural) color and some very nice surface options; soft press is perfect for gumovers for instance, and the its texture doesn't get into your way even with smallish (8x10") prints.
Definitely try it (sulfamic acid treatment and FAEW)!