Experimental tape-head flux generator – looking for head dimensions and mechanical standards

I’m experimenting with building a small magnetic flux generator for reel-to-reel replay heads.

The goal is simply to see whether it’s possible to characterise frequency response without relying on a calibrated reference tape. Whether it actually works remains to be seen!

To build the fixture I’m trying to find the physical dimensions of professional tape heads, particularly the Otari MTR-10, but dimensions from any Studer, Ampex, Revox, Sony, Tascam, etc. would help.

Has anyone come across engineering drawings or knows whether there were standard mechanical sizes for professional heads? Even measurements from a spare head would be extremely useful.

I’m asking the same question over in r/ReelToReel because there may be more Otari owners there, but thought the experimental hardware side might interest this community.