I have a full exhaust system for an ETZ250 for sale. I bought it to replace the rotten one on my bike, but the head bolt had siezed itself in the head and I stopped there. I got given the bike for free so if you want you can take the bike for free too otherwise it's just going to get scrapped.
i would have applied a blowtorch to the alloy head around the exhaust port & expand the metal, this with the oil already in the threads would have loosened the nut.