Well..it's not just 90. You clean the threads. The teflon paste the heck outta the arp bolts and bottom them out. Don't follow the turn til they stop instructions if you want the exhaust to fit. lol (I learned the hard way).
Then once the teflon has a little time..I copper sprayed the new gaskets on both sides a good thick couple layers, put them on, head on and then 40...50...60...70...75...80..85..90 ft lb torqued them down.