fantastic!! imo the red belts make the sportings, i've been wanting to do this to my sei for a while, will look great with my red and black leather seats im planning too!
Its a simple straigtforward job to do the fronts as its just the actual belt that you change.
And changing the belt on the rears is simple to, but if tour changing the receiver bits as well thats abit more fiddley and you may have to undo one of the seat mountings, so i wud say bout a couple of hours with no problems.
You can leave the old stalks and stuff, but the belt bits just swap over. Do be a bit careful if they're the pre-tensioning ones as they have to be disarmed (and re-armed). Easy enough to do, all in the Haynes.