Summoning
@Package4 ... By my very amateur knowledge of uniforms, it appears to be authentic... Though most likely post war considering a few reasons. One is that it looks to be machine stitched on the top part of the band connecting it to the body.
While my knowledge of buttons of the time is limited, I've only ever recognized those style of buttons on post-war gear... I may be wrong on that regard however.
Also, while I'm sure that golden chinstrap braid was probably used
some time during the Civil War, that is once again something I've seen on most post-war caps.
I will say, the "Chief Engineer" stitched braid is something I haven't actually seen before. While I've seen similar braid designs and even things similar to the crest (or, whatever it's properly called), I've yet to see something that long, and with two words... Very minor but unique in my point of view.
Keep in mind, there are more actual experts in this field here on the forum. Take my response with a grain of salt.
Cheers,
-Seth