This really should be easy.
As I said earlier, field does not go by voltage rating, but by current rating. Luckily tho, ohms law works so V=I*R.
So you should be able to measure the field and get R=V/I=220/2=110 ohms as verification.
Now just run the motor on the Dc field weakening control drive of your choice, up to 1400rpm with a solid 2.00amps dc on the field winding. You should then be able to measure about 440vdc on the armature, confirming nameplate data. Armature amps of course will be low since they have little to do with speed; they just make torque.
Now watching your tach (speed). since you are at armature voltage (and supply) limit, it will not change much - especially if you have properly programmed the drive for 1400rpm, 440v, 2amp field as base speed.
Start reducing the field amps from 2.00 down; this will make the speed go up. Continue reducing the field amps until you get to 2800rpm - THAT is the min field amp setting for this motor and like I said above, will probably be somewhere around 0.7amps (I thought about it some more compared to other similar size and range motors we have done in the past.) Really, this number SHOULD have been on the motor nametag as 2/.7amp.... Might you have missed it somehow? Maybe it would be good to paste up a picture of the nametag?