Adv- you asked a bit ago about solving that "gap" between the seat and tank. I don't see any possible remedy short of a completely custom seat that cinches up tight to the rear of the tank, and "climbs" the back of it, or cutting and re-welding your hoop. Or a custom tank. I think the hoop mod is probably the easiest remedy if you must fix it.
Personally, I'd live with it. Once you paint and coat the frame and tank to your final scheme, it will go away a great deal more. This issue is the only thing the gives me the stick about 550 tanks. I have a few early models and the opening at the rear is problematic for mounting or custom seats. The later tanks seem to wrap the top down much farther, and have a really nice, "rectangular" line to them. But I don't prefer the gas door from them. Heads or tails?
I'll be spending the late fall/early winter cutting, re-welding, and glassing my 550 to fix my gap, which I never would have done except it have to re-paint it anyway. This "issue" is one I've tucked away as a caveat for the 500/550 when I go custom on them.