I am pretty sure most of the parts from the b16 and b18 block are the same but i have seen these two blocks side by side and the b18 block was taller. The two blocks looked identical minus the height difference.
Now I found a engine rebuilding/performance shop that sells ARP head studs that fit B18/17/16. The part number corresponds with the kit ARP says fit the B18c1. I guess all the studs are the same length. I was concern b18 studs would be longer than b16 studs due to the block height difference but I guess this is good news.
T.E.D. Components
Now about the nitrous I would probably be all right with a stock set-up but I though just to be safe and while I have the engine still out I might as well put a new head gasket on.
I don't know about your comment SRHguru of nitrous being safe at any compression level. A stock compression engine can handle a small shot of nitrous(50) but i would think twice before popping a 200 shot on a ITR. But maybe thats just me.