Is the tensioner screw look like a large screw in the bloke that requires what appears to be about a 15MM Allen Wrench / Hex Key ?
On my 1983 Alfetta GTV 2.0 the lock bolt had a normal Bolt head and standing at the front of the car this bolt was on inlet side of engine at front and towards the top of the head itself. With the camcover off it would be very obvious.
There should be two bolts (nuts), one each side of head, just below each cam about 9/16 or larger on which they used to mount the A/C bracket.
Just below the bolt on the the inlet side there should be the smaller tensioner Bolt .
NB the 'official' method uses 1 to 3 above but instead of manually moving the car, you allow tensioner to take up slack using just it's internal spring' . Then Retighten the bolt. Put cam cover back on and warm engine and whilst it is smoothly idling at about 1000 RPM, slightly release tensioner bolt so that the slack is finally tacken up. I do not like this method as things can go wrong if you release the lock bolt too much or the engine speed varies whilst the lock bolt is unlocked!.
Alternatively, if you think the tensioner 'should' be free to move then you can release the tensioner, move car slighly forward , in gear ,so that engine rotates slighly and takes up the slack and then whilst holding the car steady so that the engine does not move any more (especially 'backwards' ) retighten. This does not require a new gasket if it works as you do not need to remove the cam cover
I have ripped this picture
form another Site
and it shows the lager 2 bolts/nuts on th e engine that I was refering too...
the lock bolt should be just below the one on the inlet side i.e towards the person looking under the bonnet. (hood)
NB it is possible that the large Bolt/nut each side of the head is actually an Allen key 'bolt' on your car. Either way, the lock bolt will be slighly below and slighly to towards the centre of the engine and will probably be 1/2" A/F.