For first starts, my preference is to put the damper at 20-25 BTDC and then time the distributor accordingly.  With the breaker point ignition and with the rotor in the neighborhood of coming up to the #1 post in the distributor cap, turn the distributor housing clockwise to where the breaker points just crack open.  The rotor should be pointing at the #1 post in the cap.  You can now tighten the distributor.  I would much rather have the timing liberally advanced for first starts rather than be retarded which can cause the engine to belch, cough, or spit fire when attempting to do those first starts.  Once the engine is up and running and the camshaft is broken in, you can check the timing with a light and adjust accordingly.

Lorena, Texas (South of Waco)

Ok, I note, at that time described, the dots open and close just before aiming for the cylinder 1 pole, is this correct? . At those 20 ° BTDC, is the dealer with the spots open or is he already aiming for the cap post on cylinder 1?

Hopefully this gets through the English to Spanish conversion without getting too distorted.
 
The rotor pointing at the #1 post in the distributor cap is a secondary effect of where the rotor is aimed as a result of the points just starting to open.  That’s assuming that the distributor is stabbed in the block so it will have the rotor aimed at the right spot in the cap.  It doesn’t matter where the #1 wire is in the cap as long as the rotor is pointing to that particular spot once you have the distributor housing adjusted to that spot where the breaker points have just started to open.
 
Because the rotor normally turns in a CCW direction, you will need to turn the distributor housing in a CW direction until the breaker points just start to open and no more.  It is when the points just crack open as to when the current to the spark plugs is generated.  The more the distributor is turned past that point where the points just opened, then the more the timing will be retarded.  If the rotor is not pointing at the #1 post in the cap and instead is pointing to another cylinder when the breaker points just crack open, then either the housing or the distributor shaft will need to be turned accordingly to make that happen.

Lorena, Texas (South of Waco)

I don't want to mess things up a lot at this point, but I do want to do the right thing. I think I understand the explanation, I have the mark at 20 ° BTDC. Well the distributor, I have it in place with the rotor pointed at cylinder 1, I turn the housing clockwise towards cylinder 2 and when the points begin to open is where I lock the housing.

Following Ted's articles
http://www.eatonbalancing.com/blog/2009/06/12/spark-plug-indexing/
http://www.eatonbalancing.com/blog/2009/06/11/spark-plug-side-gapping/
I have acted accordingly

A little help

That looks like a Boddingtons to me. Enjoy!!

MplsMike
'56 Parklane
Minneapolis, MN

There is less left to return it to the truck

The same, friend👍

As long as the rotor is pointing at the #1 post in the distributor cap when the breaker points are just opening, you will be good.

Lorena, Texas (South of Waco)