N scale Kato diesel Loco body shell removal tips

I have several new Kato C44-9W and SD70ACE n scale locos and haven’t been able to remove the body to facilitate decoder installations. I have taken the shell off Atlas units without incident, but the Kato units seem to be built a little differently, and I am worried about damage if I attempt this in the wrong way. Anyone have some helpful tips or links to info on this?