Hi there, unfortunately, I do have some experience with what you are going through - not neosporosis, but lemme explain..
Last year this time, I had a 9 week old female, she developed the neurological symptoms. It appeared like she had a stroke one day during a nap. She had trouble walking on one side, I understand how hard it is to see..My vet put her on prednisone first to see if she possibly bruised her spine. The prednisone helped a TON. She was almont back to normal..until the pred stopped. I tested for everything, including Neosporosis. She ended up being negative for that, but I did research about it a lot. Starting on the Clindamycin ahead of time is good. Better to treat it incase before the blood results come back. Did your vet do blood work for this? If not I recommend they do so. Long story short, once she was off the pred, she went downhill VERY fast. Went blind, deaf, and couldnt walk. I took her to a neurologist and she ended up having Hydrocephalus - which was a result of her getting a brain hemorrhage in her brain stem from having a difficult birth, I believe. She had to be put to sleep just shy of 4 months old. Not to scare you here, but you should really see a Neurologist, JUST in case. I wish I would have seen one right away.
Anyways, here is some research about Neospora.
Treatment of canine pediatric Neospora caninum myositis following immunohistochemical identification of tachyzoites in muscle biopsies
Overview of Neosporosis: Neosporosis: Merck Veterinary Manual
Hope your puppy is on the mend soon!
EDIT: any chance he was bitten by a tick? Ticks can cause tick paralysis.