Correct, the 1252G probably has one module with 3 antenna slots on it.
If you had the 1252AG, then I believe it would have 2 modules, with 6 antenna slots.
The typical 2.4 ghz antennas are rounded all the way around the antenna
The 5ghz antennas however are kind of square shapped around the antenna. I think it basically has two flat sides and the curves around between them. Do you have a part number for the antenna?
2.4 is b/g/n - more common
5 is a/n - less interference
I really can't answer for the 5ghz antennas on a 2.4 radio. I'm pretty sure that there is a Signal Attenuation issue when your antennas don't match. It might work, but probably not as optimally as it would if you had the correcct antenna