To make a 2MT to 3/4 x 16 Adaptor, you need to get a 2MT stub Arbor and machine the cylindrical end to a 3/4 x 16 thread of the appropriate length and thread form (Presumably Whit? )
Arc sell a 2MT soft Arbor with a 1" diameter x 1" long end, with a 3/8 BSW drawbar thread, so you will need to buy a 3/8 BSW screw in tang as well
Locating on the 2MT should provide good concentricity of the thread and the register.
Howard