The 123GT had one of each as standard so if your lights were fitted from new they were just following the fashion. You might be able to find a matching spot but a NOS pair by Bosch or Hella are not too hard to find and not too spendy. You can use existing wiring, hopefully set up with relays, for the new lights, with small changes to make them come on at the same time. Legally, if set up as long distance lights, they should only be on with main beam.
B20A, A cam and single carb, is very usable in day to day driving with good torque low down. This makes normal driving very easy with top gear being usable below 30 mph.
"Tom" note the info below your sig. I doubt if you want that displayed.