You will want to rough up the inside of the idler clasp and the outside of the idler drum for better adhesion to keep your idler adjustment in place. Springs are useless, if you get something caught in the track to make the springs work, it'll also probably break the track link. Also, if your track set has the pins going in from the inside, take the time to remove each and every one and insert them from the outside. Track pins tend to walk out a hair and it only takes a hair on a KT for the head of the pin to catch the rear plate as it goes around the idler, which will also break a link.
Attached are photos of a rear hull brace you can make from simple brass plate. Since the photo shows a much older KT hull than you have, simply make the plate flat to bolt to your hull sponsons on each side. You can also use the plate to give extra support to the upper real hull since you will no longer have the hull flex endemic with the stock hull. You can put another cross hull brace on the front of the hull, but be careful to position it to clear your transmissions.