The one hazard with adapting to standard filters is that at some size point the filter and/or shade begins to obstruct the viewing lens. I've first hand experience, having adapted my 124 G to use a Series 7 89B IR filter that has been in my possession for decades (those are about 60 mm). The shade is more likely to be the problem in that scenario. Being so close to the lens, the interference is more ghost-like and wasn't too bad to deal with unless you had critical details in the bottom of the composition. There are some new plastic Bay-1 filters appearing on ePrey from time to time that seem to work OK. They are inexpensive - Authenticke Rollei filters show up too, but they tend to be a bit more dear.