I am still unsure about this. It seems half people say lock the cams on the bench and half say on the car. The Peugeot manual says on the car and this makes sense to me to avoid potentially 'knocking' valve heads putting it on the car.

I'm confused which way is best???

I would pin it first everytime just so you can see what you are doing.

Just be carefull when placing the head that you dont catch the open valves on the top of the block.

Also to add that having played with a good few of the Rs heads it does sound like something isnt quite right with the amount of force you say you need.
If I was you I would take the carriers back off and start the assmebly again, they really shouldnt be very difficult to turn with a socket or spanner.

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Ryan