At this point, as stated above, the only change to the PS-2 Steam Upgrade kit, is they remove the PS-2 board, battery, battery harness and heatsink kit and replace it with the PS-32 board, and heatsink kit.
Diesel could be the same, but they have not released it yet. I think Diesel upgrade harness are the hold up.
As far as fitting they are similar other than connector location and height as compared to the PS-2 board. There are some small locomotives where speaker is in the frame not in the fuel tank, or short tenders where the fit may be interesting.
As an example I am doing a repair to a 5V FF electric. The shell is not tall and the speaker is inside the engine. Despite a very long chassis, the room to place a 3V board is tight, and it looks like I need to mimic the upside down mounting. With the 12pin connector elevated over the speaker edge. Not sure if the PS-32 to will fit. To be continued, and I will post pictures. But it will work for much of the conversions and repairs, and it also can work with the PS-2 slave boards. Actually has a 2 pin connector that is used for the motor signals with better output. G