Given the clarification from the OP, here are some of the oldest crossings I've been to...
These two in Nashville have some old NC&StL signals at them, though the US&S cantilevers, US&S 8 inch lights, and the US&S Teardrop bell at 19th Avenue are the only original things:
http://www.rxrsignals.com/Tennessee/Nashville/18/
http://www.rxrsignals.com/Tennessee/Nashville/19/
This crossing in Portland, TN has a Transport Products Corp. mast that probably dates from the 1950s, but just about everything else is from the 1960s, it appears:
http://www.rxrsignals.com/Tennessee/Portland/Main/
This crossing in La Vernge, TN also features a pair of old WRRS signals from the 1950s/1960s, though the original bell and one of the gate mechanisms were replaced:
http://www.rxrsignals.com/Tennessee/La_ ... nes_River/
Another old L&N install from the 1960s here in Tullahoma, TN, though the original lights were replaced:
http://www.rxrsignals.com/Tennessee/Tullahoma/Brown/
Christiana, TN also has a really old Transport Products Corp. signal from the L&N, likely installed in the 1950s, with all but the gate mechanism, gate arm, and gate lights being original, though the other signal was replaced at some point:
http://www.rxrsignals.com/Tennessee/Chr ... hristiana/
As far as old signals still in service in Georgia go, here's a few old L&N installs from the 1950s/1960s that have at least one of the original gate mechs intact, though two of them also have the original lights and another has an original bell:
http://www.rxrsignals.com/Georgia/Grays ... raysville/
http://www.rxrsignals.com/Georgia/Marietta/Mill/
http://www.rxrsignals.com/Georgia/Marietta/Waverly/
In Alabama, there's also a few old crossings.
Here's an old L&N WRRS install from probably the 1960s with the original bell and one of the signals having been replaced:
http://www.rxrsignals.com/Alabama/Bridgeport/CR96/
This L&N WRRS install from probably around the same time has had all but the bell and signals themselves replaced at it as well:
http://www.rxrsignals.com/Alabama/Calera/CR84_2/
Huntsville has a couple of old L&N WRRS installs (most likely from around the same time period as well) still in use, with almost all of the original equipment there:
http://www.rxrsignals.com/Alabama/Hunts ... ily_Flagg/
http://www.rxrsignals.com/Alabama/Hunts ... b_Wallace/
Odenville, AL has an almost pure SAL signal at it, from the 1950s at the latest, though its partner across the street was replaced by CSX in the early 2000s:
http://www.rxrsignals.com/Alabama/Odenville/Alabama/
Another almost pure SAL install from around the same time:
http://www.rxrsignals.com/Alabama/Ohatchee/Main/
This one is also a rather similar situation, though the vast majority of the lights at it were replaced:
http://www.rxrsignals.com/Alabama/Ragland/Church/
Irondale, AL also has another mostly pure SAL install from the 1950s at the latest in it as well, though the original bell was replaced at some point:
http://www.rxrsignals.com/Alabama/Irondale/2/
This one in Guin, AL, features a Transport Products Corp. "No Left Turn" signal from the 1950s, most likely:
http://www.rxrsignals.com/Alabama/Guin/US278/
Birmingham, AL has quite a bit of old equipment in use still as well:
RACO cantilever signals from what's most likely the 1960s:
http://www.rxrsignals.com/Alabama/Birmingham/24_2/
http://www.rxrsignals.com/Alabama/Birmingham/25/
And old Transport Products Corp. signal from the 1950s (most likely):
http://www.rxrsignals.com/Alabama/Birmingham/16_1/
Some old SAL installs from the 1950s at the latest (though the original bells and one of the signals were replaced):
http://www.rxrsignals.com/Alabama/Birmingham/50/
http://www.rxrsignals.com/Alabama/Birmingham/56/
And old L&N(?) WRRS install from the 1960s at the latest with most of the original equipment having been replaced:
http://www.rxrsignals.com/Alabama/Birmingham/24_1/
Of course, that's for the crossings that I've been to that are on the site.
