Originally Posted by DIMcyclist

Strangely, this is right up my alley, being the fruits of the research I've been doing on my oddball Panasonic...

If you can find them, the '83 to '85 MB-3s are a closer match to the Atlantis in terms of geometry than either the Stumpy or, say- an MB-1 or 2, as is the '85 Fuji Boulevard XC, which has a much nicer DB Valite tubeset (I seem to recall reading somewhere that Valite tubing was custom-drawn for Fuji by Ishiwatta).

Each of these are fully lugged framesets and have more road-ish geometry- with steeper head & ST angles and more BB drop (55mm for the Fuji; 60mm for the MB-3)- than an average MTB. This also makes them excellent candidates for 650b conversions, if you feel like going that route.

Also, Bridgestone's CB series matches that general profile in some years, but not in all; most of the time the CBs were basic MTB-derived hybrids, with the attendant shorter chainstays & high BBs.

You might also look into the '84 & '85 Miyata StreetRunners, which have similar geometry and probably the best frames of the lot (Fuji's Valite is nice- it's stiff & resistant to corrosion, but it's also heavier for being vanadium rather than cro-mo; that is, actual tool-steel).

If you don't mind the higher MTB BBs, check out the '85 Trek 850/70: long wheelbase and lugged, DB Tange Prestige tubing.

The closest match for the Atlantis is (of course) still Bridgestone's XO series; the Atlantis' direct ancestor. With the exception of BB drop, their geometries are very nearly the same, and they're all designed by GP.

If you feel like going the serious vintage/ collector route, look for an original Bridgestone Atlantis Mk 1, or the even earlier Eurasia & Diamond frames (mid-to-late 1970s; the Diamonds were quite sexy and the Eurasias had biplane forks, although both had hi-ten tubesets). Bear in mind, these were true randonneur bikes came in 650a, 650b, and 700c versions.