Adding preamble sequence to unknown data in mil_std_188_110B appendix_C

As i am trying to implement Mil_std_188_110B appendix_C standard in simulink,after scrambler block i need to add the synchronization preamble with the unknown data. Symbol rate of the scrambler block output is 2133 symbol/sec,after adding the preamble the symbol rate(unknownddata + synchronization preamble) should be 2400 symbol/sec.

The data frame structure is

(256 symbol unknowndata+ 31 symbol preamble + 256 symbol unknowndata+ 31 symbol preamble + 256 symbol unknowndata+ 31 symbol preamble + ...)

To have 2400 symbol rate for above frame structure ,

1) What should be the symbol rate of preamble ?

2) How to do timing for calculation of number of unknowndatasymbols and preamble symbols ?

3)If the data rate of unknown data after scrambler block is 6400 bits/sec(3 bits per symbol) ,what should be the data rate of preamble ?