The kind of valve spring compressor that hooks on the camshaft should work. I'm not sure there's room for the kind that grabs the lower coils and pulls them agaist the upper retainer.
Is there a reason you're replacing the chain and tensioner? M103s are not knows for throwing chains regardless of mileage unless foreign objects are involved.
I don't know what a scott bottle is but it might be easier to stuff rope in to the combustion chamber to keep the valves in place. Make sure the rope isn't the kind that sheds. The manual says to give it 5bar which is around 70psi.