I believe we are talking about the same system here.
http://www.summitracing.com/parts/ho...t/model/blazer
Let me start by saying that I used a set of full length of Summit racing headers on my 72 Jimmy along with some cheap turbo mufflers. I ran into a few problems.
The instructions indicate that the exhaust should be installed under the frame rails just outside the transfer case. This didn't work at all for me because the pipes wouldn't clear the rear cross member and I didn't like the thought of it being that visible and open to getting crushed. I ended up running it above the transfer case and beside it above the cross member. This required cutting and welding to get the angles right. From there back it fit great. The tolerances were tight and it just cleared the axle, gas tank skid plate and everything else.