@Howick Reach cannot handle higher voltage coming back, but most injectors do break the power line, so it should be okay.
Tallysman TW155 looks like a suitable injector. If you want a splitter for two receivers there is Tallysman TW150 that passes power on one port and blocks on another. They also have a couple of other models.
I have all this running now. Base unit is connected to a Rojone 36dB antenna and Rover is sharing an antenna with my ag guidance GPS. I also have the TTL to RS232 converters working and am getting the required communications between base and rover through Elpro 905U-D radio modems