How about some close ups of the hitch?
If your going to go to the trouble of making a 3pt, it only makes sense to build the attachments to the correct spec. It's not big deal since you're building them from scratch. Not making it to spec is like building a trailer that only hooks to your own truck. Just doesn't make sense. If you need the spec for the width and height of the hitch along with proper pin size, here it is. I suggest a vertical pin height of around 12"-16". Maybe someone can tell you what some of the manufactured attachments are.
3 point Size chart.jpg