Tony old pal, the only thing that has to be loosened off is the bracket that holds the downpipe to the bell housing. It would probably be enough to unbolt the bracket from the bell housing, remove the downpipe, loosely fit the bracket to the new downpipe, bolt up the new one and then bolt up the bracket. You should be able to undo the bracket from the top of the engine bay and certainly the turbo connection from the top. Stainless Steel downpipes are frowned on as they are more prone to splitting than Mild Steel in use. All the best, Peter