Belt Buckle Custom Blank

I'm trying to create a blank belt buckle that can be milled locally. Belt has to be made out of stainless steel and allow for interchangeable/one size fits all (adjustable strap). Leather strap would be cut to length and one end clamped into the buckle. Other end with punch holes to fit over the post on the buckle. Dimensions of the belt would be 80mm length x 55mm width x 10mm height plus additional height for the brackets to hold the clamp for the strap. Strap width 38mm Strap height 5mm The attached images include buckles with logos already milled into them. I need the top of the buckle to be a solid flat surface so we can mill into them to a depth of 3-4mm. The other images include the clamp we would like attached to the buckle to allow the belt strap to be attached to the buckle. I'm open to ideas to simplify this but the keys to this project are that the belt buckle must be made of stainless steel that can be milled into a depth of 3-4mm and have somewhere to attach a strap that isn't permanently attached.