Is there a way I can clean these up and reuse them? Are there any risk in using old shocks?
I let mine soak in a tub of Metal Rescue for about a week and they turned out pretty good. They weren't quite as rusty as yours, though. Take them apart and see if the springs are as badly rusted under the chrome covers. If not, you can flip the springs upside-down after you clean them up to hide the more rusted part under the cover.
These shocks can be disassembled and reassembled. If you want them to look new, rechroming will be required. The problem is they are about 35 years old and well past the sell by date. Modern shocks perform much better than the original shocks ever did. Consider an upgrade. If it was my bike, I would get it running the way you want it and then go spring for a new set. I really like the Hagons on my '72 450. They have the period look and ride very nice.