Hi @geotopoagro,
If you already have 2 RS2+, I’d pair them up over LoRa. In this case, the baseline can reach up to 8 km but is dependent on obstacles and can decrease in densely vegetated areas. We have a support tip on how to configure LoRa on Reaches well.
As David said, UHF radio is made to work with RS3 as a rover and a 3rd-party base. The baseline and the conditions will depend on the power of the base radio.
As Tim mentioned, you may consider using the RS3 as a rover with your Reach RS2+ base due to its tilt compensation feature.