I have an 07 UC and have a Road Glide seat on mine. I've test fitted a few seats and minus a small gap between the seat and the tank trim, they fit fine. Any 07 or older touring seat will fit. 08 and later have different mounts and will not fit 07-earlier and vice versa. 07 is weird year too because it's the changeover year for some stuff. For example, I have a cush drive on mine. It's confused a few people.

 

2008 while still the old frame did have the seat mounts changed to the new frame type so newer seat will fit it. Yes a SG seat will fit on your Ultra. Those seat were made to look cool not ride well but your ride have at it. The 08 is year they stared adding some of the new frame parts like seat mounts and TBW ect Not 07.