Upon googling 'sidebone' for some images for you, I found I was mistaken to think it's necessarily too close to the front of the foot to be sidebone - never seen it anywhere that bad myself, but there is at least one pic there showing a pedal bone with the side bone almost up to the extensor process - mid toe! So yes, it seems it could well be sidebone!
Afraid I don't have a lot of experience with severe ringbone, but in my experience and from what I've been told by others, so long as it's non-articular - meaning not interfering with joints - it can be quite... impressive & not cause lameness.
Articular ringbone on the other hand, being in the joint, can be quite debilitating, and possibly the only answer to it once it's advanced, is to help the horse put up with it until the effected pastern joints actually fuse, at which time it stops being painful. *There is some anecdotal info to suggest horses can partially recover from it, with correct movement allowing the bone to remodel back, wearing away the excess ossification, but not sure that cartilage can grow back at all, so... I personally know of one animal that was diagnosed with it - tho without xrays(?), who had very little movement throughout pastern joints, but did improve enough to regain more flexion, be paddock sound & able to run with his mates again.
I would personally want xrays and to get his feet well balanced & functioning, consider using boots rather than shoes(poss only low profile, as high may rub) if it is non articular or so far minor joint issues. I'd want to find some 'experts' - vet, farrier, etc, who is experienced with it - not just the creating/diagnosing either!<GG> I'd also put some time into studying these conditions, hoof function & soundness generally and the pros & cons of different approaches for it. I wouldn't fret about articular stuff too much, as if he's not at all lame, hopefully if it is present, you'll have caught it early enough to halt or at least slow it's progress with good management.
Anyway, that's about the extent of my knowledge of it, so sorry I can't give you more!