To me they implied infantry because they mention a regiment beating its drums and sounding its trumpets.
Edit: The regs state "trumpets sounding or drums beating" which would make one think that they are talking about cavalry and infantry.
The regs don't mention bugles at all, and only mention trumpets once or twice. The band is never referred to as anything other than the "band" while the musicians are not enumerated by instrument but, rather, are simply referred to as (company) "musicians." It may be one of those details that everyone "just knew."
Drums are much more prevalent than trumpets in the regs, and "beating" calls far outweighs the "sounding" of calls.
I have read that the bugle was adopted by the army in 1835, however fifers were also still in use by the army and marines during the Mex-Am War. The National Park Service has a picture of two army musician re-enactors, and one has a fife, and one has a drum.
So, I don't think there is a ton of information out there, and I have not found anything that lists the number and type of instruments for a regiment's non-drummer musicians. I think it is safe to assume that each company had a drummer as one of its two musicians.
