Marley -

This is just a hunch - but I think you Atala is mid-sixties issue.

Why?

1) The stem just seems right, and I'd surmise original. The later 3T stems like yours said "Made IN Italy". The early ones said "Made Italy", as does the one on my late-sixties Ganna (the date of which was pretty well corroborated by Ganna in Italy).

Yours makes no mention of Italy at all, which makes sense if you were previously manufacturing them in the home market, for the home market.

2) I think it is more probable that someone in Italy way back then thought the "wild-west" logo was appropriate for this market, then that someone here could ever locate such an aftermarket "Atala" decal. (Not a lot of demand for those I think.)

Anyway, unless someone can peg the manufacture date from the S/N, I don't think there is a whole lot more to go on here... (Eg; The Japanese components are not OEM and I think your bike probably came with Valentino or something like that. (That is to say, the Japanese DR's are quite an upgrade!))

Whatever the date, it is all-in-all an interesting bike and a great dumpster find!