He should save his money for when something actually needs attention - and it will eventually. I see nothing wrong with changing the plugs, inspecting the cap and rotor, replacing if necessary, but the rests of it is over the top. Valves don't require adjustment. I've never heard of replacing a head gasket as preventative maintenance. A 103 motor timing chain with 157k is nothing. I once had one replaced at 280k and it was original in perfect condition. I've had two mechanics tell me since that you just don't tamper with a working factory timing chain on a 103 motor. The replacement is not likely to be as sound as the unmolested factory original. Tell him to be patient - the car will create something that actually needs to be done.