I just had the same problem today installing my headers on my 87 350 tbi... I un bolted the bracket(had to cut one of the bolts). so then the bracket comes completely off with a little finagling or pulling on it with some vice grips. then got manifold off. then bolted header up. then I had to cut one of the mounts for the bracket that would have bolted on the header because the headers weren't meant for that bracket. by cutting one of the mounting spots of the bracket it it allowed the bracket to still hold the power steering but not have to bolt on to the new header. this also had air conditioning pump though, BUT I have a blazer with 89 tbi and headers with same bracket as you and if u want I could take some pics or look at it and let u know how its mounted with the headers.