If the chain were off by one tooth the valve timing will be off about 16
to 18 degrees. Does that allow the pistons to hit the valves - I don't know.
A chain that's run 270,000 miles is very tired and suspect. The chain
not only wears but also stretches. The rule for the old 3.0L 617.XXX
five cylinder turbos is that the chain should be replaced if the crank
shaft angle is 5 degrees (or more) when the camshaft is at 0 degrees.
The measurement is made on the 617.XXX engine by rotating the engine
until the notch in the thrust collar that's immediately behind the chain
sprocket of the cam is aligned with a groove cut into the first camshaft
support's left side (0 degrees on the cam). One then reads the crank
angle off the scale on the crankshaft's vibration damper (where the belt
drive pulleys are located). Your engine may be a bit different but the
principle will be the same. This check will also determine if the cam is
correct or off by one tooth on its sprocket.
Finally, in closing, this engine is getting close to the mileage where
it will need an overhaul so it may be worth considering, depending on
the condition of the car, either doing a full overhaul, or doing nothing
until it breaks and then making the decision to overhaul it, install a
used engine or scrap the car.