Those necks are bolted on. The only glue they use is on the fretboard. Anything can change, but that's how I've always seen them, and I've re-set a few of their necks over time. In a traditionally made guitar I like the button installed on the back of the body, right behind the neck heel. I usually drill a larger hole in the back itself, and the smaller pilot in the dovetail. Then the screw "floats" in the back, which is fragile, but threads the heel block. Seagulls have a bolt down there towards the end of the neck heel. That means you can't use too long of a screw because it will bottom out at the bolt.
Because of the shorter screw I'd say put it in my second favorite place-the neck heel. I'd go with a screw that has about 1/2" (3/4" at the most) protruding on the other side of the strap button. There's no wood to put it to the side of the neck. You'd have to be so close to the neck that you can't get your strap in there. Some guys put it on the underside of the neck heel, like where your palm would hit if you were playing up high. I don't like it there for that reason alone, but structurally its fine.
I hope this helps, but what kind of an idiot writes two paragraphs on a strap button anyway?