In a spec script - it's probably best avoided. You're not making the film, so, just like camera movements, it's not up to you what song gets played. You should perhaps just describe the style of music... Bob takes a record and places it on the record player - classic rock emanates from the speakers....
If the script is for yourself, do whatever you please. Even if you can't get the song you want, the title of a song may help you remember what you were thinking at that time.
In the script for "Beavis and Butthead Do America" Mike Judge wrote that the hallucination scene should be set to "Fire" by The Crazy World Of Arthur Brown. In the end he went with White Zombie's "Ratfinks, Suicide Tanks and Cannibal Girls", probably due to the fact that Rob Zombie animated the scene!
