NIK SAYS THIS WAS DONE WITH THE HEAD OFF THE ENGINE.
When I was doing some more assembling of my engine (finishing a complete rebuild), I arrived at the time to put the stock manifolds back onto the head. Behind the intake manifold, there are two clamps that hold the bottoms of the manifolds to the head. Well, after about twenty minutes of fighting to get the clamp onto the stud, then fighting even more to get the nut started onto the stud, I figured it might be easier to start them onto the stud before placing the intake manifold on the head. Then while holding the clamp out of the way, slip the intake manifold behind it and onto the locating pins. This way, the nuts are already started and all you have to squeeze into that small space is a wrench.
GREG ROWE GIVEs US SOME POINTER ON HOW TO DO IT WITH THE HEAD ON THE ENGINE.
Do you have the original Triumph bolts? The head of the bolt is about 1 1/2" long (sticking out) so that you can slide your wrench (spanner?) up and down until you find sufficient clearance to move the bolt a small fraction of a turn.
I used an open end wrench (no special tools) with no problems - if you consider only a small fraction of a turn at a time no problem.
Clean the threads with a wire brush or a tap so that the bolt turns easily and you will be able to thread it most of the way on by hand.
Make sure that stupid clamp thing doesn't spin out of position or you will have to do the whole thing all over again.
Be prepared for your back to ache like an SOB the next day.