I have done it in my 01 Silverado. Used the seatbelts out of a OBS ext cab with no 3rd door, and weldd in reinfrcements to floor and b-pilar. Can't post any photos right now from my phone....

I asked the same question all over every forum I could think of over a year ago when I did it, and got very little reply or answers, other than a handfull of guys with caged trucks!

I am not going to claim what I have is necessarily the safest thing to do, but it's in my weekend truck and I typically only ride alone anyway. And yes, I did drop quite a bit of weight too, even with having to fab my own custom brackets.