Hi Paul,
Don't believe your ssb radio is stable and accurate enough for Aero Selcal decoding.
However with demo software you can give it a try.
Some info:
SELCAL Decoder
General description
The SELCAL supports aero selective call (ICAO, Annex 10). It needs, that the receiver has been set to the correct frequency. The frequency error should be less than 10 Hz to provide correct decoding. The SELCAL consists of 2x2 tones (duration 1 sec), according to the following specification:
Designation Frequency (Hz)
A 312.6
B 346.7
C 384.6
D 426.6
E 473.2
F 524.8
G 582.1
H 645.7
J 716.1
K 794.3
L 881.0
M 977.2
P 1083.9
Q 1202.3
R 1333.5
S 1479.1