Lex Orandi, I think you have some leeway here, depending on your devotion to the saint. A very few memorials have proper antiphons (St. Martin of Tours, I believe, is one example). But generally the memorials come from the commons, in which case the antiphons and Psalms of the day are perfectly fine. It would be equally fine to pray the antiphons and Psalms of the commons (using Sun Wk I for morning prayer). I would do this latter if I had a special devotion to the saint.
The intercessions can come from either the day or the commons.
The reading and responsory, and the collect, should definitely be either from the proper or the commons for a non-optional memorial.
I don't think one can correctly take the antiphons and psalms from the common for a simple memorial. This is the rule given in the GILH
Memorials During Ordinary Time
235. In the office of readings, at morning prayer, and at evening prayer:
a. the psalms and their antiphons are taken from the current week and day, unless there are proper antiphons or proper psalms, which is indicated as the case occurs;
The common antiphons and psalms given in the common are usually for feast days and solemnities. So, for instance the memorial of St. Dominic, if he was the prinicpal patron of a city, would be celebrated as a solemnity in that city. In this case, the common antiphons and psalms would be used.
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