75 through 77 had a bad habit of letting oil leak past the rings into the left cylinder if on the side stand. If you find it on the side stand and not the center stand you will have some issues for sure on the right cylinder. Meaning make sure you put oil in that right cylinder for a bit before you ever turn it over, it may be dry as a bone. The left will be full of oil.
The GL1000s are not worth much so go slow, don't dive into it with both feet. The gear oil in the shaft should be fine but the front seal is probably gonna leak on you. It may swell back and be kinda okay once you get it wet and spinning again. Forks and shocks should be fine. Tires will be horribly dry-rotted. Brakes will be find but the hoses will be weak.
Honda tanks are pretty good. Slosh it out with alcohol or spirits and see if brown runs out of it. It may be fine. There are numerous tank treatments out there if its a bit rusty. It has a standard pitcock so that is easy to deal with.
