MGA Model SA-80 AM/FM/8-Track Stereo system

I found this MGA Model SA-80 at a Flea Market near Baltimore for only $1.00!!! The unit works just fine, picking up FM stereo stations with ease, and AM works perfect. The 8-track player works also and the unit is very, very clean, it must have been stored for years.

Im trying to figure out the year of manufacture for this unit. Unable to determine by the serial number (#6402722) or the model #(MGA SA-80). The speakers are model MGA Model # SS-11. I'm guessing between 1972-1978, so any help would be appreciated!! Also, does anyone know what the acronym MGA stands for? I know they were a division of Mitsubishi Electronics, and they had an office outside of Chicago in Lincolnwood, IL. I'm guessing that Mitsubishi built the unit in Japan and had MGA market it in the U.S.