I think the precaution about backlit scenes is a strong indication to me that there will be halation in some conditions.
Any CD3 film processed in a CD4 developer or vice versa, runs the risk of degraded color and image stability. It is the nature of the game. I've done both, but I know what I am up against and I take my chances. It is the nature of the game called chemistry. It is not going to ruin things utterly, but you may not get the entire result you deserve.
It is an admirable effort and deserves credit. It also deserves a try..