[Suicide Junkie]

And if u think for example what then is to stop someone building a bigger ship with smaller engines ahhh well those smaller engines will be a lot easier to destroy than bigger engines,

With the mounts, you can enforce the larger ships = larger engine, no problem. You don't even need armor or economics to stop abuses.

What you do is have the engine component too large to fit on any ship, and use the mounts to shrink them to the appropriate size. Use the "minimum size" and "maximum size" restrictions to allow the mounts only on the specific hull they were designed for. (So no escort engine mount will appear for a heavy carrier)