@Goonley I published a 15 step tedious process to.make a custom rig a few days ago its here on the forum in the BoneBreaker topic. Its painful, but it does work. Less painful without feet and a face, but still kinda painful.
if you have no issue when importing both, import both. The. Try to re-import using the newly created skeleton.
of that causes shrinking too something is wrong somewhere in the import.
If not, then the original Skelton is bad/not scaled or something…