I don't see the reasoning behind stuffing a 6.3 or a 6.9 down the throat of a sl/slc aside from the 'Hillary factor', i.e., do it because its there. If one wanted more hp, ergo, more performance, would it now be a much better use of time and money to install something like a 5 lt. Ford? One can easily get 300-500 hp out of these engineswith not all that much effort and cost? To spend 30K in 1973 style dollars to get an extra 50 hp seems like trying to buy bragging rights rather than trying to make a useful car. Granted, the installation is a work of beauty, but, God, what a waste of resources.