
Apart from whether or not he's an outstanding example of his breed, with significant wins in whatever you do with him to support that, you really don't want to let him be used at stud, even once, because once Pandora's Box is opened, he will be looking for the next bitch which, unless he is a top winning dog of his breed, won't be the there. I know it sounds negative, but really. Right now, what he doesn't 'know' he isn't missing.
You would need to get the non-breeding endorsement all good breeders put on immature stock they sell as pets, lifted - no endorsement? Then with respect, he may not be from good bloodlines much as I'm sure you love him. With our first hound, we were convinced we had the next Crufts BIS on our hands. Of course, we didn't! He should have his Hips and Elbows scored too, remembering that the owner of the stud dog is 50% responsible for the puppies he might sire.
And further, without the paperwork, nobody with a good quality bitch will be interested in using him because they can't register the puppies with the KC. And to do that yourself, you'd need the registration numbers of his sire and dam, at least. Assuming they were KC registered!
Again I'm really not trying to be negative, but you would be way better to just keep him as the much loved pet I'm sure he is.