I'll offer what I know of my early eighties (?) Mirage as well. Though it no longer exists in it's original form I have retained much of the original components.

I'd say there is a need, as finding specific info and attempting to date this Motobecane led to much frustration and ultimately settling for only a general idea about it.

I'm still not sure what the hell Motolite tubing is composed of - and if, in fact, it's what this frame is made of.