No, I don't think you can do this. I think your buck-boost (2-0.75kVA open delta) will have a rating of 12.39kVA. The input current would be 34.4A at 208V-3ph. 450.4 says that the autotransformer shall be protected at not more than 125% of the input current (or the next standard size up.) This would be 45A.
norsky63: Is there a typo in your original post? I do not see how even three single phase 24 volt boost transformers or a three phase 208 to 24 volt isolation transformer can convert 208Y/120 to anything but a very strange near-230 delta with possible neutral problems. Which would be within the motors operating range, but still on the low side. (230 volt rated NEMA motors really expect 240 supply, IMHO.)
In any case, that would ONLY work with a closed delta on the output side, not an open delta, since the third output phase wire would also have to be offset from the incoming phase voltage.
If you are intending to use a 120 to 24 volt isolation transformer or autotransformer on each line to neutral leg to convert the 120Y to 148Y, in hopes of making use of the 256V delta that could be formed from the L1, L2 and L3 terminals, then it would theoretically work, but be nominally too high a voltage for your motor.
When you say that the motor is rated for 230/460 delta, you mean that it is a six winding motor which has the option to be wired parallel or series for use with either 230 Delta or 460 Delta? Because there is no such standard thing as a 230/460 supply.
Executive summary: It can be made to work, and the transformer rating would only have to handle between ~1/8 and ~1/5 the power rating of the motor, but it will really confuse anyone who has to work with it later, possibly to the point of being dangerous.