i've got 'em in my 89 yj. i don't care for the design much. they go under the oil pan. you have to loosen/remove them if you need to do work under there. if they went back a little further they'd be fine.
installing them i had to jack up the jeep and put a stout rod under the back corner or the flange and lower the jeep to get the rear bolt to line up.
i also had to cut two extra manifold gaskets up because of the diffrence in flange thickness between the offenhauser intake i got and that of the pacesetter. it could just be that the offy flange is really thick.
maybe someone else has some experience with a stock intake manifold. they seemed strong enough, but i've also never installed headers before that.
there not bad for the money, but a slightly diffrent design would be better.
i did have noticeable increase in power, but the offenhauser intake and a new carb was installed at the same time. so, i'm not sure what the increase from the headers alone would be.