My Io started as a Signature version with two power supply chassis and volume controls. I have not heard the Eclipse mod, which uses "stealth capacitors." Where the stealth caps are in the Eclipse mod from Aesthetix, mine has V-Caps. The power supplies in mine are chock full of Black Gates.
Since I have not directly compared the Eclipse and GNSC modified versions, I cannot give you details of an A/B.
Turn around times for mods from Great Northern Sound vary according to the then current level of modification activity. This one was a lot of work and took a couple of months. The total cost of the mod was $5,000, but my mod cost more than others may because of the two power supply chassis on mine. If you have a single power supply chassis, or you have different requirements, your mod costs will likely vary.
Great Northern Sound Company is in Stillwater, Minnesota and has a website at www.greatnorthernsound.com with all of their contact information if you want to go and check them out on the web.