Cam Timing - Engine Won't Turn!

[Thorn]

Are you using the cam caps from you own cylinder head or the ones that came with the replacement?  The cam caps are machined in situ at the factory and are not interchangable, they have to go back on to exactly the same places they were taken from. Easy to refit them in the wrong place as they are all similiar with just arrows point to the right side.
They could be out of  line enough to prevent the camshafts turning when the cam cap bolts are tightened.
Were the caps loose when you recieved the head, if so they may have been removed and put back incorrectly?

Oops, good catch! I've actually been using the caps from the old cylinder head, I didn't realise there would be quite that much of a difference. I'll try the correct cam caps for the head tomorrow before I do anything drastic!