1997 Questions for all other cars timing

I have a Peugeot 406 2 litre 16 valve petrol which had a broken cambelt. I bought a replacement head as the valves on the original were bent. Without the head, the crank turns faultlessly. With the head still off, the camshafts turn faultlessly. But with the head on, and the timing pins through the relevant holes in the crank and camshaft pulleys, the belt in place and tensioned, the engine will only turn about 160 degrees.

To check there was nothing accidentally in the combustion chambers, I removed the head but found no fault.

With the belt off, I can turn the crank 360 degrees if I turn the relevant camshaft a little whenever there is an obstruction so I suspect the pistons are either hitting the valves or the inlet valve is interfering with the exhaust valve. In other words, I think it is all to do with the timing but there is only one place to put the pins through the pulleys so I can’t understand what’s wrong.

Help please.