The 900 has 2 transformers - one to couple the ribbon to the headamp, and another to couple the headamp to the output cable/preamp. It's conceivable that the Bulldog transformers could replace the first one, but whether it would change the sound for the better would be a crapshoot IMHO, without knowing the specs of the original transformer and/or a schematic of the mic.
Maybe Oliver will know.