[Porsche-O-Phile]

I would bet money you're buying new valves. I'd recommend checking the piston crowns very carefully. Same with the valve guides in the head - they're cheap to replace "while you're in there".

Most likely you can get away with keeping the pistons but I've also heard of a broken t-belt busting the valve and causing enormous damage to the piston/cylinder. You probably don't have that situation but until you open it up and look, who knows?

Assume the worst, hope for the best.

Absolute worst case you're looking for a new block (or rehoning), pistons, valves and a head. Most likely just valves.