Okay Chass is a friend of mine so I feel the need to defend him a bit.....
First - Chass, you should of NEVER said it was sprinkler pipe! that gives people the idea that the material is something light weight and weak. Sure its still pipe but .....
Second - Its not finished and you should never post anything on POR with clearly stating its not finished or you are sure to get flamed......
I think its fine (will be when its done)!!!! Now granted structual tubing (DOM or HREW) is better but Pipe is way cheaper to buy and to bend.
I did mine out of Pipe if that tells you anything. (before I cut it off for lack of highway performance issues). If I was to do it again I would make it out of Tube but only for the purpose of I NOW have the tools to bend tube and tube is lighter. Anything up there is better than nothing IMO. Well almost anything, you could have made it of conduit! The key is that it NEEDS to be built so its strong, So you know it will hold up in the event you do flop it. And you also need to NOT put yourself in high risk situations thinking your fine since you have a cage, because its still only pipe. And people have got to understand that a cage like you designed is to help protect you and the vehicle from low speed flops, not 60+ mph barrel rolls or rolling the vehicle down big hills.
As for materials of 1 1/4 dia x schedule 40 Pipe (1.660 OD X .140 Wall) : I think what you used is probably A53 Grade A pipe (thats the low quality pipe). Its got a yeild strength of 30,000 psi and a tensile strength of 48,000 psi. The stuff we used on Project Blu which is 1.75 OD X .120 wall AISI 1010 HREW mechanical Tubing has a yeild strength of 58,000 psi and a tensile strength of 63,000 psi.
So with this comparision the material the pipe is made from is about 50% the strength of the tubing material we used on Project Blu. But now you also have to consider the cross sectional area since the pipe and tube have different dimesnions. The Section Modulus for a hollow circlular cross section is Z = 0.098 * (OD^4 - ID^4)/OD. so for your pipe its .23417 in^3 where the tube that we used on Project Blu was .23408 in^3 which is almost the same. So for this case, the pipe is truely about 50% the strength of the tube since the crossectional strength is nearly identical. Pipe is about 2.2 lbs a foot and the tube is about 2.1 lbs a foot. So in that case a pipe structure will probably need about 50-75% more material to be close to the same strength as a tube structure.
So the question is it safe..... I think for mild use it will be fine. Mild use would be flops on the sdie of the vehicle. but if you roll the vehicle down a hill it will probably shift and move into teh cab. I highly down it will CRUSH the cab. you will also notice that if you look at my exo that I did out of Pipe I put a lot of braces all over it because I knew I needed more material on it to make it strong. plus I was trying to cover the rear of my 4runner so the hollow space was much larger which makes the structure weaker hence another reason for more material.
If you feel leary about it, pull the doors off (so you don't break the glass) and flop it over in your yard and see what happens! Seriously! If your worried about it taking damage or crushing the cab, then you shouldn't be driving it with that exo. now granted I never flopped mine over on purpose (or even on accident) because I was worried out it shifting to the side since I couldn't cross brace it on the 4runner, but your truck is cross braced. On Project Blu we thought about doing it but by the time the cage was finished we already had fuilds in everything and we where rushing to get it down to myrtle creek. Also I don't think Pete liked the idea very much but I'm sure it would take it. Also the only way an exo is more unsafe than no cage is if it breaks in a manor that it puchers the driver or passenger IMO. Teh more steel the better. Sure you might flop more often with a exo cage due to the weight, but atleast you can still drive the vehicle.....
BTW, I'm offer the use of my winch if you flop yours over.
Also here is the one that I made out of pipe for my 4runner that I was refering to.