Time to rebuild?

No, the '73-up factory (and factory-type replacement) chokes are not adjustable. There are no R or L marks, and there's nothing to rotate. If you want to be able to adjust the choke thermostat—which is very handy for dialling-in appropriate cold-start and warmup behaviour—then get a № 1234 Electric choke kit and drop it on. Take you about 20 minutes, and is a large improvement over the primitive and notoriously cold-blooded factory '73-up choke setup.