FLEX uses an FSK or 4FSK modulated signal at either 1600 or 3200 baud
for a total of four different data rates. Data is interleaved and
BCH(32,11) encoded as well.
While the frame format and protocol is well documented by Motorola, the
preamble data sequences which indicate the immediately following frame
format are considered proprietary trade secret information. It IS
available on the Internet if you search for it, but since it isn't
documented as legally reverse engineered, it is questionable whether you
can distribute it in the US jurisdiction.