Why does proximity to the CXA1145 save me the 75Ω load terminations?

Also, what about that V REF on the CXA1145? If it turns out to be a virtual ground halfway between the CXA1145's GND and +5V then can I use a connection to V REF as VG in the circuit?

Terminations are needed on coax runs whose lengths are a significant percentage of the shortest wavelength in the spectrum of the signal. With a 5MHz signal, significant reflections won't occur on a transmission line unless the line is several feet long.
As a compromise, you can source terminate (75Ω in series with R and B at the CXA1145, or those resistances may be internal to the chip), and eliminate the load terminations. You should be able to run the Y input directly to the Y buffer on the new circuit, avoiding the need for the emitter follower mod.
You might be able to use V REF on the CXA1145, but I don't know how "stiff" it is. You could try it.
If we make changes, resistor values will have to be changed. The CXA1145 datasheet is not good enough to design an interface circuit without playing with the chip first.

 

You might be able to use V REF on the CXA1145, but I don't know how "stiff" it is. You could try it.

I can always buffer it in the normal way. At least it saves me that voltage divider for vg.