When I did mine, I got ARP head bolts from summit & they came with a sealant/lube. I'm no pro so I cant say that's the best but, its what I used & haven't had a problem yet.
I got the same grease with my ARP studs, but no sealer. Permex makes a thread sealer (not their locker) which sounds like it'll do the trick.
Has anyone used gasket sealer on their threads?
It depends on what kind of "gasket sealer" you're talking about; there are many different kinds. Silicone can work, but it is not entirely reliable in my experience.
I have ARP bolts and used their Teflon sealer. It's like a grainy white plumber's dope and I think it may affect fastener torque readings less than other sealers.
The "dope" on the threads only will do the trick. I have used both Permatex thread sealant and regular ole pipe dope on head bolts and both seem to work about the same. I had no leaks with either.
I stopped using the teflin based liquid sealers a few years back, I use black permatex on the lower bolts....make sure you clean the threads are clean.