9.2 grains of Trail Boss will fill the case half full. 14.8 grains will fill it 80% full, which is about as far as you want to go. Both instances assumes the bullet is seated one caliber deep. Do not compress Trail Boss, even a little. Accuracy will go to pot. I'd expect velocity to be around 1,650 fps for the starting load and 1,850 fps for the max.
Trail Boss is becoming very popular for reduced loads because of it’s ability to fill cases, negating the need for fillers or special shooting practices - like raising the muzzle between shots in order to “pile” the powder atop the primer.
The NRA publication Handloading has reduced loads for the .30-06. From a 24” barrel a 155 gr cast bullet with 14 grains of SR4759 will give 1245 fps. 20 grains will give 1715 fps. The Whelen and the .30-06 are so similar I would consider the starting load safe, and work up to the max. You may find the max load needs to be reduced a few grains due to the Whelen’s larger expansion ratio.