If you look at photo DSC_0029 you can see the serial number and the model number M0001D (which is the EDU 512ke). The 512ke was introduced in April 1986 and came with a 800K floppy drive standard (according to Mactracker) and was discontinued in Sept. 1987. The Plus was introduced in Jan. 1986 so there was an almost a 1.5 year overlap hence the 800K drives in the 512ke