Dimensions of a Space marine miniature's armored neck-collar

[Lucerne]

What would the specifications in size/shape be for the collar ring (with the three holes) that's at the top of Space Marine miniatures? What size would an equivalent be for the Primaris marines-ie: that'd fit inside and instead of where the current flared collar is and how wide would the ring be between the outer and inner surface?

 

I'm looking to try and see if anyone'd make commissions of such a-relatively simple- cast in bulk on Shapeways or something- I'm using Primaris as a basis for oldmarines and am not above shaving off the collar and replacing it for proper Truescale Aquila/older armor design collars.