When I did the head gasket at the same time I replaced ALL the vacuum tubing including all the "T" & "Y" connectors. So I am fairly sure the leak is not a vacuum tube.
While the head was off I detached the intake manifold and replaced the gaskets/seals between the head and intake manifold. THEN it was relatively easy.
Now with the whole thing reassembled I couldn't get in there.
Your suggestion to cut of a short pc of allen head is good - that may work. I'll give it a try. I had to do the same thing for my R107 motor mounts (& also some other tough to reach bolts).
Regarding torquing, I'll tighten while the engine is running to see if I get any change - if I do then I'll keep tightening till the vacuum stops leaking. If I don't get any change then I'll stop tightening and take it to my indie (we'll find out if he has a smoke machine)