12v and 24v heads are diffrent and wont fit together mate i think u guys got the 12v in the mk4 with a switching manifold that my be worth investigating
i agree with most of that math but mine would never reach mid 80s just tootling round unless i was sat in heavy traffic and since the lower temp thermostat it wont reach 80 hehe i treat 70 degrees as safe vince at stealth backed this up