I'm with David; Marine uniforms are something left to Marines.

Having said that...if you're still set on altering a Marine dress blue jacket, then look for an officer's jacket: no red piping to deal with. Also...for what it's worth, (at the risk if my fellow Marines' ire,) a Marine jacket minus gold buttons, red piping, rank and insignia is pretty much just another high-necked coat. I think they were originally patterned off of the British anyway...

Best of luck with your project.