Yes, you've got it.
For some time now, I've been using the steel thin jam nuts with aluminum split lock washers. The gaskets are the Moroso Perm-align blue types that do not leak, at least on my application.
Now I have acquired aluminum thin jam nuts and will use them with the aluminum split lock washers for a complete valve cover mounting system. The aluminum studs get inserted into the heads using a good lock-tite adhesive since I remove the covers every now and then to adjust the valves.
I'll weigh them later and post. Should be good for an ounce or two. I know it sounds crazy, but I'm counting 'em down one at a time here, there, everywhere.
Of course, some fasteners either have to stay steel or at the very best Titanium because of their strain duty. All of this has to be calculated correctly to work and survive in such an evironment.