The early clutches 75-77 had a rather heavy action. Honda listened to the criticism (eventually) and made alterations to the later bikes from '78.
They changed the L/H switch to one without the clutch lever perch and fitted a different lever on the 78-79 which makes a huge difference. I have gone even further and rigged mine with a hydraulic clutch from a GL1200 but that is a lot of work for some, but not a huge, gain in lightness over the later set-up.
Sometimes a bit of general maintenance will help a lot. A new nylon or Teflon lined clutch cable, properly routed, will help.
If your cable looks OK, try removing it from the lever and undo it from the clutch end (no need to take it right off the frame), use a small funnel or make a funnel shape from scrap plastic taped aroung the lever end with something to hold that end up in the air, wrap a rag around the other end to catch any drips and fill the funnel with some light oil (not engine oil, that is usually too thick).
If the bike has been sitting for a while the plates have a tendency to stick together. An oil change and some use will usually sort that out.
Get the cable adjustment right. There are at least two adjusters on the clutch cable, most times three. One at the lever, one in the middle inside the false tank which you may have to remove the air filter to get at, and one under the round black cover at the back of the engine.
This last one is the most important and the one that folk usually miss. Take the cover off, there is a screw and locknut inside, slacken the locknut, turn the screw in until it just touches, back it off about 2/3 turn and tighten the lock nut. Take most of the excess play out by the middle adjuster and fine tune with the lever one.
If you wish to convert your early bike to the later spec you will need both the new switch and a clutch lever set.
The GL1000 switch is no longer available, but you can use a switch from the CB400F part number 35150-377-013, which is still available. This has exactly the same functions but the wiring colours are different.
The lever perch is 53172-431-780. Levers are available from many eBay sources at lesser cost then the OEM one.