Referring once again to Paul Boyers excellent book 'The Rickenbacker Bass, 50 years as Rocks Bottom'. He states in the chapter dedicated to finishes that Montezuma Brown was only available between 2003 and 2006 (it first appeared as a Colour Of The Year in '03 and was the only colour programme to be extended). Therefore the OP's bass, being a 82, can't be Montezuma Brown.
Pics from the book attached- 2 Monte Browns and an Autumnglo & Walnut comparison. The latter are very close in colour, however the accompanying text states that Autumnglo disappeared from RIC price lists in 1980 but Walnut continued until early '85 although it was described as 'shaded brown' from '81.
I'd still be inclined to say the OP's bass is Walnut.