How hard it is to install L98 Alum heads and a set of hedman tubular exhaust system headers with the engine in the car.....

 

Its not all that hard, just very time consuming. Youll need to pull the whole intake off, as well as all of the accessory brackets. The headders are the easy part, only takes a few hours. I would start by taking out the stock manifolds and y pipe, then the entire intake, then all of the accessory brackets. Once all of that is off, youll need to unbolt the heads, which isnt really a problem. If your goin down that far, why not pull the water pump and radiator and put a cam in there too? Its only a few more hours work.