No, loosening the TWO bolts will not allow you to turn the distributor
unless you completely remove them. They are mounting bolts.
The bolt I am talking about is a pinch bolt that requires a 7/16" wrench
(11mm may work) and it is about 1 3/4" further up and tangential to the
distributor stem.

If you are just turning the crank to find the timing mark so you can put
the chalk mark on it for easier visibility, it doesn't make any difference
which way you turn it - whichever is closer.

Yogui mentioned disconnecting the vacuum - I don't do this. I leave it hooked
up because the 20° compensates for the smaller advance when the vacuum is
disconnected. If you disconnect the vac advance you will have to adjust the
idle much higher to keep it running, and then when you get the timing set
it and the vac hooked up, it will be idling much too fast, so you gotta set
it back down. My method keeps you from having to do that and also makes it quicker and easier.

If you KNOW how much your vac advance advances, you can add that to the
setting they give you with vac disconnected, and leave it hooked up.
For example, 5° vac advance +15° = 20°total that you should get with it
still connected, so if it has vacuum and you leave it connected and set it
to 20°, you'll have the required 15° with it disconnected (but there is no
good reason to disconnect it).
--
George Downs Bartlesville, Heart of the USA!