Are you supposed to retorque the head after a few hundred miles? If it's showing signs of having been honed then there's a possibility that wasn't done? I'd be checking the cam box oil seals for weeping and replace them too. Disturbing the cam boxes and replacing gaskets there may lead to noisy tappets and the need to reshim them so leave well alone if the head is good and doesn't need a skim. If it does then so be it, valve stem oil seals at the same time, check the valve stems aren't bent when the head is off too. If it ran fine then they ought to be good and it's just a head gasket. New cam belt and tensioner bearing and alternator belt whilst it's all apart?
Tensioner bolts - I always used the spanner flats nearest the bracket, not the outer one when removing it. Less chance of shearing the head off. Somewhere I have a long handled, thin, straight, single ended spanner for the job. First used on my first car when the starter cable stretched and the pull lever stopped working. It was possible to push the lever on the starter motor from behind the car to get it going. (name that car!) but it is equally useful for removing and refitting a Beta tensioner spring!