Ahhhhh, well for Kato I know the Enterbay doll's mask comes on and off of his face, his hat comes off and hair pops on in its place with magnets, if that helps at all for Kato!!
He's basically pre-made Kato with all the accessories and whatnot, but if you're looking to build Kato from scratch, I'm at a loss.
Personally I could see making really good "grab bag" (did I use this phrase before in here last time? I think I did? XDD) customs in that you perhaps say, take the RAH set and pop on Enterbay's Kato head, and buy the Captain Action costumes and plop the GH costume on your PTE guy, but I have NO idea as to the level of customization you want. I'm a "path of least resistance" kind of gal. If something is presented to me on a silver platter, I'll take it (i.e. "Change the hairstyle and expression of this guy and pop a few buttons and you essentially have this other character"), and I only do what I feel I need to do in order to make the custom I want.
Unfortunately most times that's a full custom anyway!!
One of them is a Big Money Project because I need to pay someone $300+ for a custom 1/6 sculpted head, there's no way around it. *Sigh* My sculpting skills are nowhere within the realm I want to make myself happy with this head.
Oh, speaking of, depending on what you want to drop, having a custom head made is an idea as well.