Unless you have a penchant for doing burnouts to impress Burberry clad teenage girls, the standard clutch is absolutely fine for this sort of power. The reason for replacing the clutch and slave cylinder/release bearing assembly is because they do wear (obviously) with use and it's a fairly expensive labout job to replace them as the subframe still has to be dropped to remove the gearbox.
A new waterpump doesn't hurt. The originals had plastic impellers. To be fair, most of them are ok, but the new part is all metal and it's not very expensive.
Those and the tubular headers are probably all that's really worth doing while the engine is out, although obviously a new set of proper Motorcraft platinum spark plugs should be fitted since the rear bank is slightly awkward to reach in situ.
If you want to make sure it's running tip top and not burning spare fuel, then generic Zirconia lambda sensors cost about 15 quid each on Ebay. Fit those into the new headers using your existing Ford plugs rather than swapping your old sensors in. Lambda sensors do degrade a bit with use, but most people leave them in situ until they fail completely. They do provide the measurements the ECU compares the fuelling with though, so you could lose performance and money by running excessively rich on old sensors.