Hi!
Give us a wee hint what's going on here! Is this to be sent over your own bearer or what?
But ordinarily you send your PCM stream on a pretty tight basis, with about as good attention to timing as is possible since relativistic effects are important here. PCM timing comes from atomic clocks.
Most modems used to synchronise to the bearer using a decent pll, when I studied this sort of work, and the data was conveniently loaded into a set of shift registers set up as a pipe in which words can be placed from the side. In the modern day I expect this would be carried out in a logic array.
(or did I miss the point?)