What problem are you trying to resolve here? As long as the replacement speakers are the same ohms as the ones you are removing, and you wire it up correctly, you shouldn't hurt the amp, but I don't understand why you want to run the risk of messing up the sound of a cab you "love".
The idea that you can replace half of a 410 which you "love" with 2 speakers from another 410 that you also "love" and you'll get anything close to the sound of either of the boxes is not very logical.
I'm on the side of the fence that says, if you're not unhappy with the sound of your Ampeg, why spend money to mess it up.