First photo shows the fixture in the vice, second photo is the 30 NMTB and 30MM side by side, third is the fixture on the vice, fourth is the mill itself.
The fixture is just a block of steel, of unknown variety, bored to accept the 30 NMTB taper and the round drawbar part. I use a bolt to draw it into the fixture to hold it tight.
The fixture has an arm with a lug on it that goes into the slots on the taper shank, after cutting the first pocket loosen the draw bar bolt and index to the other slot to cut the second pocket.
I use an original 30 MM end mill holder to set up the fixture in the vice. I set the table stops once I have the fixture centered and a cutter seated in the pocket. I set the depth stop also with the cutter seated in the original. I lock the table so it doesnt move, then I put the 30 NMTB shank in tighten it up, and use the quill feed handle to plunge down nice and easy. I use carbide end mills also, I think its 7/16 but you would have to measure, been a while since Ive done one and dont remember. Hope this helps, any questions feel free to ask.