Hi,
I would say you will be very lucky to get a stud cat who as lived outside, to stop spraying in the house. I can`t understand why the person you had him from, didn`t check how you was going to keep him. As stud cats kept outside need appropriate housing with heating. You can try useing animal disinfectant and keeping litter trays as clean as possible, but you are going to be very lucky to stop him now.
Regards Amanda.