In all seriousness, how bad does it look?
That type problem is usually caused by a fouled carburetor... one cylinder running too lean, however, it could also be due to a weak (or no) spark on that cylinder resulting in what we call a "wash out" condition. Either situation will tear a piston up.
The exact scenario can't be known until the powerhead is completely torn down pertaining to the pistons and cylinder walls... boring, sleeve replacement, etc.
What is known is that at least one cylinder needs boring O/S along with the O/S Piston. The other three = ? until final tear-down. One cylinder head, Failing ignition components = ?
Common parts = spark plugs, piston rings, PH gasket set, carburetor kits, Water pump, Thermostats, Gear lube, spray paint.... and there's always the unexpected, "blue" bearings to name one... there will be others.
Average labor time = 24hrs, includes run out, adjustments, etc.
The cylinder head replacement... if when cleaning the head of all the piston rings particles embedded in it, one little sliver is missed... that sliver will glow like a glow plug of a model airplane engine which will result in pre-ignition that'll melt a piston in a short amount of time... not worth the gamble.
NOTE: The "spray paint"... Always, when the powerhead is assembled, including cylinder heads and intake manifold... paint it to restore its appearance to new condition, otherwise, it has a patched up look (ugh!).