Depending on how the signal leaves your B3, it may do damage to the 147. Even though the 122 and 147 have the same input connector (6-pin), they are expecting different types of signals. The 147 is an unbalanced input, i.e. one lead is the signal, and the other is the ground, pins 1 and 6, respectively, if memory serves. It expects an unbalanced output from say a Leslie Preamp pedal. The speed control is 110VAC switched to pin 2 or 5. The 122, however, was designed to work specifically with the Hammond organ, and as such, expects a balanced input, Signal-1 and Signal-2, for instance. Furthermore, the input is decoupled from the tube grids with a cap to allow for an approx. 80 VDC control signal to "ride" on one of the Signal lines, and act as a control signal to switch between fast and slow speed. This was done to accomodate the 5-pin Hammond connector (not enough pins for all the signals required, when speed control is considered. Mr. Hammond did not appreciate the competition for tone cabinets from Mr. Leslie and wanted to make it as difficult as possible to interface the two units, hence the pin incompatibility, which Leslie solved rather elegantly, IMHO). So, you have different options but the easiest is the change the 147 amp front end to replicate that of the 122 amp, by:
1) rewiring so that it is balance input
2) adding the decoupling cap
3) changing the relay from 110VAC to 80VDC
Note: this information is from memory, and it's been awhile since I've fussed with this stuff, so please verify the details independently, or get a technician to make the change for you if you are not comfortable wiring line voltage circuits.
Hope this helps!