Terry,
The advice is that a boiler should be examined unclothed at around ten yearly intervals at the boiler inspector's discretion. Most will be relaxed about this if there are no signs of leakage from under the cladding and no signs of movement on visible surfaces. Ten years fits well with the four yearly hydraulic test intervals as you can see. If the boiler hasn't been steamed then my fancy would be that you would just need the routine hydraulic and steam test, but if it has been used then expect the inspector to want the cladding off. Unless it shows signs of having had repairs then 1.5 x wp with the fittings on will probably be acceptable, otherwise a full 2 x test.
If this is a wide firebox with nothing hidden between the frames then you might get away with removing the cladding and leaving the boiler on the frames.
Talk to your inspectors before you do anything.
Eddie