Hello John: I'll try to briefly answer your questions:

1. suggest you start watching eBay as these items used come up often

2. likely either the needle valve inside the float bowl is worn if the source of the leak is coming from the float bowl top relief valve or the leak is coming from the metering jet, at the bottom of each SU carburetor (or both!)

3. horn ring is attached by a single set screw, on the back side of the steering wheel. Once off, you probably only need to ensure the horn wire is attached to the metal horn ring, without taking off the plastic "V". The horn wire travels through the inside of the steering column, exiting from the bottom of the steering box, then to the horn relay. Check this for electrical continuity

4. grill is held in place from inside the radiator cavity, so I'm sure you need to remove the radiator, unless you can see the attachment brackets and screws, anywhere up to 12 screws to remove.

Keep your questions coming.....
--
Cam a.k.a. CVOLVO.COM