Do you not possess an instinctive revulsion when presented with an idea so gruesome?
I'm curious... do you find this idea to be significantly more gruesome than harvesting organs from a dead body and using them in a different living person? Or how about using organs from other animals as transplants in humans?
Personally, those seem more gruesome to me than if I had a spare kidney grown for myself from my own DNA. You even noted that growing single organs would be more acceptable - so how about if they grew a kidney, liver, pancreas, gallbladder, and stomach at the same time? The slope is getting very slippery now - add a few more organs and we're nearly to this replacement body concept!
FWIW, I'd oppose this project, but it's more because I don't trust them. I don't trust that they know what sentience is or how to gauge it, nor whether or not their creations small brains still have it. There's a whole lot more that can be done in the meantime, and I hope that will help prepare us for these dilemmas.