Furuno always tries to develop new products with backward compatibility in mind.
But sometimes new technology makes that desire unattainable. The gearbox you mentioned is not compatible with the NavNet 3D, but the array (antenna) would be.
However, it must be matched to the proper DRS. (Digital Radar Sensor)
The radar you mention is from our NavNet 1 or vx2 system. The RSB0070-059 is a 6kW radar and comes with a 4’ antenna. (XN12A/4) and our RSB0070-064 is a 4kW radar that comes with a 3.5’ antenna. (XN10A/3.5) If it is the first model then you would need the DRS6A, less array, to use your existing antenna, or the DRS4A, less array, if it is the latter.
If you do decide to use your current array please make sure to specify to the dealer you order it from that you want it less the array. The DRS4A and DRS6A come standard with the array so it has to be specifically ordered without it.