Is the broken bolt in the head? If so you are basically screwed unless you can find a 6" mechanic to crawl down in there. I assume that this in on your slc and if it is like mine there isn't room to change your mind along side the exhaust manifild. This is one of those 'might as well' situations that can cost you big bucks. If you have to take off the head, which won't be cheap even in you do most of the work yourself, then you 'might as well' do a valve job on it, in which case you really should do both heads. Since you will have both heads off you "might as well" do the timing chain. I "might as welled" myself into a $1,500 overhaul on my Diesel truck when a $20 oil sending unit wourld have solved the problem. Be careful.