Search for sk30 standard, its the same as bt when it comes to the taper, the only thing that's different is the inside contour and the drawbar gripper. You can get proper dwg drawings from acrow, they carry normal bt grippers and ott style. ott cost the same so I'd go with them, also because its a pain to get mas403 drawing standard, and ott makes sk30 readily available. if you want accurate toolholders just download the 3d models from sandvik coromant, if you make the taper angle correct in your cad you can add an assembly constrait that will mate the tapers perfectly together without an error.
On another note, I'd go without rigid tapping and instead do thread milling with multiple flutes. Rigid tapping has size limitations on top of torque and synchronous action. In my opinion not worth the trouble. With thread milling you can machine any thread size and if you use multiple flutes it can be as fast as rigid tapping.