Nope, i re-used the gasket. That's the old head lol. The one i put on is all nice n clean. in fact i think it had had a nice chemical wash not so long ago as there isn't even any oil discolouration.

Didn't lap the valve in as both it and the old one were in pristine nick. even the old carb head one was not pitted at all much to my surprise.

And nope I didn't rotate any of the engine without the belt all timed up properly. I took it off and put it on as per the Haynes manual's instructions ie set the engine to tdc 1st.

Soooo at a bit of a loss.

Turned the cam around a bit with the head off then put it back to it's marker at the top too. All valves and lifters seemed to be doing their job fine when i did that.

Wouldn't it be evident all the time instead of just when i rev it?

it's definitley something hitting something as it's just too rattly for anything else.