[W126 Coupe] timing question

[Shayegan, Richard]

Ok, so I'm going to get down to the dragstrip next Thursday for the test
and tune night, and want to play with my timing between runs. Do I have
to check timing at idle without vacuum AND at 1500 and 3000 without
vacuum, or can I just check it at idle and assume the other values have
been shifted by the same amount. 
Also, what exactly do I have to do for without vacuum, i.e. what if
anything do I have to plug up? As long as I note where timing is now, do
I even have to bother with that? Can't I just note the current position
of the distributor and the current timing as is (without plugging the
vacuum) and just adjust from there since I don't care about the value, I
just care about how much I am adjusting by? And finally, am I correct
that all I have to do is, with the engine running, loosen the two screws
on the distributor housing, rotate, tighten them back down, and check
timing?
Stupid questions, I know, but it's better to ask stupid questions than
blow an engine.
Thanks,
Richard