I'm fine with the engines as they are. In vanilla junkers are basically a liberty faction. Sure Gallia changes this, but that's how it's been before, and as fei said, a bunch of ships have those engines.
as for mixed engines, once again i don't get it. Junkers collect scrap, make it useful, and sell it on. When exactly was it decided that they made all their own stuff out of mishmashed junk? csv is a standardised, normal ship.
The Salvage Frigate has Liberty-type engines, with the floating rings around the white exhaust. I don't know why, as the Heavy Lifter and Mining Ship both have the same color scheme and engine flare as the CSV.
It's a minor detail and I haven't ever had "Hey your engines make that ship look Libertonian" brought up in Rheinland.