NHRA rules require if you run slicks, you must have a drive-shaft loop that completely encircles the entire circumfrence of the shaft.
I dont care if you 16.50's...if you tech with slicks, and they want to have a peek, you better have one.
For the record, the factory driveshaft loops in that pic will satisfy most tech inspectors...because most of them dont know the difference between an over-flow bottle, and an empty coke can spraypainted black.
For the most part, NHRA rules are simply in place for your own safety, and that of other racers/spectators. if they want you to have a bigger loop, there is a reason for it.
they can be made/purchased/installed very easily. contact your local exhaust shop. Most of them will gladly weld up some flat iron for you. They even sell a nice two-piece design at summit so you can install a loop without removing the driveshaft.