Why are you using a Stinger system in the first place? Banks designed that system for turbocharging the NA 6.2 in the old body style ('73 - '91, such as the CUCV) and had a 2½" turbo downpipe to clear between the cab firewall and frame. A 2½" turbo downpipe will negate a lot of the power you're trying to get in this build by greatly reducing exhaust flow and increasing backpressure and exhaust heat.
If you're doing this motor install into a GMT-400 why aren't you using a 3" turbo downpipe, or even a custom 4" turbo downpipe that has been "squashed" into an oval shape to clear between the firewall and frame? If this install is into the '73- '91 platform, you should be using a 3" turbo downpipe and "squash" it into a slight oval to gain sufficient clearance.
Just my 2 cents worth.