The studs appear to be normal, the nuts appear to be stainless - so you'll need to replace them. You might look to McMaster-Carr - they have high quality Grade 8 nuts that are zinc-aluminum coated so they don't rust and will look correct on your engine. They cost about $8 a box of 25.
https://www.mcmaster.com/93827A241/
On the leaking studs: If you're willing to pull the heads, then you can use a stud sealer on the coarse threads. I use a teflon type product from ARP. I don't like to get water between the studs and the heads - causes rust, so I prefer to fix the problem at the source.
.
Other than that method, you can try something like Moroso Ceramic Seal - really good product. Make sure you follow the instructions carefully - especially related to draining and flushing the system and filling with WATER before you put this stuff in.
https://www.moroso.com/ceramic-engine-seal35500/