Welcome to the forum. Please add your location and your bike's model and model year to your profile so that you don't have to remember to tell us every time and we don't have to keep asking when you forget (see Forum Settings link in my signature).
And welcome to the world of antique vehicle ownership (they own us, not the other way around). Your bike is about 4 decades old and may or may not have had all of the maintenance necessary to keep it safe & reliable so it is highly recommended to download the Factory Shop Manual for your model (available through the CX Wiki - link in my signature) and go through all of the service procedures, regardless of whether your bike has reached the specified mileage.
I also recommend looking on all rubber parts with suspicion because rubber does not age gracefully. Check the date codes on your tires and replace them if they are over 5 years old no matter how good they look & feel (old rubber simply cannot flow around the irregularities in the asphalt well enough to grip, especially if it is cool or wet). If your bike still has the original rubber brake line(s) (should be replaced every 2 or 3 fluid changes = 5 or 6 years) I recommend shopping for modern stainless braided ones (they last practically forever and double the life of the fluid). And don't forget things like the rad hoses and the boot between the engine and swingarm (they can crack on the bottom where you don't see it).
The best advice anyone can give you about customizing any vehicle is to get it safe & reliable in more or less original condition and use it for a while before you start making any changes so it can tell you what changes it needs to make it do what you want/need better. That approach almost always results in something you actually want to keep and use but making changes based on style or on what someone else (who may or may not really understand how the changes affect the way it works) has done often results in a piece of expensive yard art that you can't stand sitting on for more than a few minutes and might even be dangerous.
Changing the forks is a good example of that and asking on the forum shows that you are thinking about the effects and trying to keep it working right instead of making changes and finding out the hard way.
If I'm reading you right you want to replace the sliders on your GL500 with ones from an '82 CX500C (they are different from the forks of other CX500 models). Both models have 35mm diameter stanchions so it would be possible to assemble working forks using parts from both but (as Randall mentioned) the GL500's axle is centred on its sliders while the CX500C's axle is mounted in front of its sliders.
The "C" in Honda model numbers stands for "factory Custom", which means "styled to look like a chopper". Choppers generally have elongated forks at often silly rake angles, resulting in trail that is increased enough to make it difficult to steer at low speeds (not to mention "chopper flop"). Honda's engineers located the axle ahead of the forks to allow the rake that the style required while maintaining a more reasonable trail for decent handling.
What that means to you is that if you use Custom sliders on your SilverWing the trail will be decreased. Low speed steering could become twitchy and it would not be as stable at highway speeds.