I don't really know much about collectors figures but I would be really careful with the conversion you suggested. These Norse look rare to me and once you cut off their swords, I'd assume they loose a lot of value. Thats obviously only if you consider selling them at a later point. If you don't I think axes would be great. And a lot more "historically" accurate (since only few people had the money to afford a whole sword). Axes would probably also make the unit wilder. I don't know why but for some reason, axes seem more savage to me...