Dynamark 12/38 lawn tractor

I have a Dynamark 12/39 lawn tractor picked up for free . I no they sold out to Murray and went bankrupt so parts and manual are scarce to none to get. didn't need a whole lot it originally had the 12hp tecushem motor when I got it someone put an 11hp Briggs and Stratton in it. Rewired everything bypassed safety switches moves and runs decent. Only thing I'm having a problem with is figuring out the year of it. maybe someone can decode the serial number to get year thanks
Serial # S004859322724
Model # C3812010
Code # 2101

April 11th 1982 or 1972.

I remember Dynamarks in the 70's for sure, but I don't recall them in the late 80's ............