Hey kush, thanks for stopping by!
I would not recommend topping any autos. I have tons of experience with Diesel Ryders, in fact I have seven 40 day old, and seven 3 day old Diesel Ryders going right now. I have topped a couple, and never will again.
If you were to top that plant, you would end up with up to 24 tops or even more, which would be a good thing if you had months and months to flower it. But with AF plants, they flower so fast that you would end up with lots of small top buds that would weigh less total than if you had not topped the plant.
So im my opinion, with Deisel Ryders especially, let em grow naturally. I have yielded 3/4oz avg in 2 liter soda bottles, and 1.5oz avg in 1gal grow bags. I have seen guys pull 3oz off of them in 5gal buckets, but that is with very nice lights, soil and nutes, or hydroponics.
Best of luck man, let me know how they turn out! ANd holler if you need anything else!
KB