Originally Posted by T-Mar

You picked it up just so I could have another serial number?

Yes, it's a 1981 model. Apparently, it was named for the Tange's new Mangaloy tubeset, which it employs. 1981 was definitely the first year for Deore but I wouldn't call it the first touring group. I'd probably bestow that honor on Shimano 600 of 1976-1977. It had an optional rear derailleur capable of handling a 34T cog and a crankset capable of a handling a 30T granny. While they are quite rare, the group also had a cantilever brake option. It didn't have some of the amenities like a 40H option for the rear hub and there were no pedals or headset but it checked the major boxes with super wide gearing and cantilever brakes.