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Im pretty sure that with a Rocky Doser, you might have to remove the PortaFilter support (fork) underneath the doser in order to fit some PortaFilters. Not sure how these are secured exactly as my Rocky is a Doserless unit but according to this article, it is probably only held on with a couple of screws so should be easy to remove and thereafter youll have heaps of room. Hope this helps :),
Just an additional thought..... If you really want to be able to use the PF Fork, it may be possible to "shim" the Fork away from the Doser using a suitable thickness of some black plastic and then refix to the Doser (might have to use slightly longer screws depending on how much you need to shim the Fork away). Cheers 8-).