Head studs for what? sr20 or KA? I know sr20's ARP won't sell them cause toda has exlusive rights, however b18c5 fit perfectly and are the same.
As for brake conversion, in a word. Lots. Finding a set of calipers in good shape around 300 bucks, then the new rotors, another 250, then the 2 choices, cheating, and using extra washers, or stainless lines, another 200 bucks... then pads, kvr are about 100 bucks. And thats just hte front. The rear is hard to do, a real pain in the ass actually. Oh, and with the new brakes up front, the stock MAster Cylinder isn't always enough, so a 300zx on is around 120-160 new, or 50-80 bucks used. So changing your brakes can easily run you about 700 bucks. I was lucky, I got full front and rear hubs, but still, no disks, no pads etc etc. OH, and if you wanna change to 5 bolt... thats harder still. THAT cost me another 350 bucks, cause I just went and bought brand new front knuckles.