Hi,

Firstly I'd be looking at the small rubber bend on the end of the inlet
manifold (that you can hardly see let alone reach!) which deteriorates and
causes intermittent vacuum leaks.  It's on the alternator end of the motor.
I've replaced mine twice with a short piece of rubber vacuum line
successfully.  It is possible to do without dissassembling things but it's
really fiddly.

If he hasn't yet replaced the ignition leads, when the plastic bits from the
plugs to the leads (inside the "tunnels" to the plugs) break down, he'll get
strange lumpiness and missing until it gets bad enough to be obvious.
Something to keep in mind.

Regards
Barry