I don't have the definitive answer for your specific boat, but... in addition to the "rule" you stated about the anti-ventilation plate (cavitation is a completely different thing) should also be set 1" higher for every 1' they sit back from the transom. I'm not sure how they sit on your particular boat.
If I'm reading correctly regarding what you stated in post #3, though, this means that your anti-v plate will sit 3" lower than it should and that can cause quite a bit of excess drag. This is assuming your current engines are set correcty. Do you have any running issues... ventilating at higher speeds, excess drag causing lower fuel usage and/or MPH numbers?
Can you swap just swap the gearcases from your current motor to the new ones? Or... also look around for used, 25" gearcases that would fit the new motors.
How much higher could the new motors be mounted (mounting holes)?
I would think a jack plate for each new motor would solve the problem, if need be, though? Although the added stress that Family mentioned should at least be considered.