I did a 16 x151 x 2 on my old 2002 zx. Kinda tight but went in without having to modify anything. Some of the guys were grinding the heads on some of the bolts by the front driver but I just stuffed mine in.
I made extensions from 3" x 1/4" plate aluminium. You can get a set from Tracks Usa for pretty cheap if you are not the fabricator type.
Don't worry about the tunnel extension. Don't need it. Trim off the flap. You can see the molding mark for a non-summit flap, just trim to that line. It also makes a cool rooster tail while running down a packed trail.
Sorry, when I got a new computer, I deleted all my old pictures of the 144 going to 151 x 16.
The track I used was from an 05 summit rev.