75 : 300 Ω Balun for 50 Ω matching at 900 MHz
For these frequencies and your particular needs, a discrete LC balun with Z transformation would be the way to go, ditching the Murata part altogether. You really should not have any issues with standard SMD stuff here.
Here is such an example, it consists of two parallel LC filters:

The way this works is pretty intuitive, the LC networks are designed to operate at the resonant frequencies, acting as phase shift networks to produce the balanced phase at output. The impedance matching can be viewed as a standard LC section providing an impedance match between 50 ohms and 150 ohms. So this should tell you a bit about the bandwidth you can expect: $$Q=\sqrt{\frac{150}{50}-1}=\sqrt{2}$$
For a centre of 57MHz:
$$BW = f_0/Q=40MHz$$
You can also use the calculator here.