Leading Edge was an OEM+ODM (they did both) in the early 1980's to early 1990's. They had a very good reputation for both quality and consistency - yes, those are doubleshots and they are ridiculously thick.
The model you have there, DC-2214, is an enhanced AT keyboard which was sold with the WinPro (486 based) systems and possibly the Model D3 (386) systems. I know for sure it was sold with the WinPro486 which yes, was AT form factor with a DIN5 keyboard. Will adapt clean using DIN5->PS/2 no modifications required. Very nice keyboards, really. Earliest actual manufacture date would be.. 1991 for that particular model as I recall, but could be wrong there.