Could be the lifters then

Doubt you would hear noisey lash adjusters echoing off a building. Intermitent sticking valve would be my guess, or a semi fluffed exhaust manifold gasket thats momentarily clearing its carbon deposits out then closing up again. Could even be a cracked EX manifold. Also, it pays to loosen the manifold support bolts a couple of turns to get a bit of movement when youre replacing the gasket. You dont need to split the manifold like other people have suggested, complete waste of time. Its easy to get at all the lower bolts, just do what the other guy said and invest in a 10mm ratchet spanner. One with a flexi joint at the ring end.

well new one is in and its all nifty,
Took from 3:30 till 6:50 or so.

Once I had all the bolts to the head undone it just opened up and I was able to pull the old gasket upwards.
Put the new one in and go from there.

Still a little miss but it seems to be fairly evenly distributed now, perhaps favouring #6 a little.

I'm also thinking that the tick is the exhaust gasket, it looks pretty crap, It looks to be made out of multiple sheets and they all seem separated, I think I'll get some headers on if I'm going to bother with the gasket lol.

Any thoughts on replacing the bolts on the exhaust side with stainless? (I don't like rust in my otherwise shiny engine bay ;->)

"I've never had to do anymore then simply removing the bolts that hold the manifold to the head.
Removing the airbox will help with access to some of the bolts and go and send a few dollars on a 10mm ratchet spanner"

What a job getting to those back lower bolts. Wiring looms, metal pipes, startermotor.. everything in the way. The 10 mm spanner too short to reach between each intake to get those little buggers. Investing in a 10mm ratchet spanner was going to be my next move.

This forum is great. Thanks for some great advice.