this is a harder Q because he is old but lived outdoors he shouldn't but he might ask vet. you should get a check up for him anyways seance he lived outdoors.
Unfortunately, he probably will. That is, IF he sprays outside now. If he doesn't do it outside, then he won't inside either. Neutering doesn't have the impact that most people think. I have had several cats that started their lives inside (only) and were neutered at a young age and they sprayed anyway...inside. Now I live in rural area and they stay outside. You might try getting him to use a litter box while still outside, but I'm not sure of the best way to do that. Good luck!
8 years is not old for a cat, if he has been spayed he wont spray, my cat is now 14 years old he still catches rats & mice & takes a bird out of the air, just had his annual check up & jabs he has been given a clean bill of health, but vet says he needs to go on a diet, as he is almost 9kg, but he don't look fat & still very agile, he was a rescue cat our last one died when he was 18, only thing ever wrong with him was he had to be on hormone tablets as vet took to much away when he was neutered