Analog inverting amplifier
It may not necessary to feed either the RF port or the LO port differentially.
One input can be connected to AC ground with the signal being fed in single-ended to the other.
If you do wish to feed the inputs differentially to get better balance and  LO suppression a center-tapped transformer or Balun (balanced to unbalanced converter) is commonly used - at RF frequencies they can be small.
A non-center tapped transformer may also be possible if the DC bias conditions of the input stage can be met.
Opamps are very rarely used at these frequencies as they don't have enough gain to work effectively.

RF Mixers - Iulian Rosu

NE602 Experiments