...BTW your Bieber avatar is awesome.-Malone
Get a long punch and hit hard with a hammer. It'll help break the tension. Then use the breaker bar, just don't twist. Get the bar and extentsion [?] straight and snap them loose.
Having just gone through this in order to install a pyrometer into the manifold I too had issues with stubborn nuts and bolts. My first attempt was to soak the bolts with some penetrating fluid and this did work on some bolts but not all. My next attempt was to heat the bolts up with a propane touch (as I no longer have a set of oxy and acetylene tanks) and melt some wax on the bolts, this causes a wick affect which draws the hot wax into the thread and I guess helps lubricate it. This also worked on some bolts but again not all. My next attempt was something I used when I did have my oxy tanks and worked each and every time, but with only having propane I didn't think I could get the bolts hot enough to make this work but it did. Heat the bolts/nut's up as hot as you can get them and then spray water on them immediately until they are cool. This shrinks the bolt rapidly - breaking them free As mentioned working from underneath helps a lot. On re-assembly I cleaned up every nut and bolt and coated everything with anti-seize before re-installing them. Although it's a tight area to have to be working in, it worked for me - good luck.