The holes are aprox 1.5" deep. Look at it this way, how many mud rigs, runing big motors and stock suspension setups do ya see blowing housings off the springs? I never have, and another thing, doing it this way, you have no torgue stretching of a U-bolt.
Like I mentioned earlier, the true/only reason for running the stock pad is clearance with the TH400 oil pan...
I don't think it will fail, if it ever does, wel crap,lol.....
It should be fine....