Here's the low down on tips.
BTW... I have never seen this posted anywhere, before.
This was done by "eyeballing" an early set of GT tips, and comparing them to an 88 GT system "on the cradle" at Ed Parks'. (This info was also verified by one of the folks, there.)
There are actually three lengths of tips. The 84-87 dual exhaust uses one short tip and one long tip. The 88 tips are identical in length, left to right, and are "medium" length.
By my estimation, there is approximately 1/2" difference between each length.
IOW, there is approximately 1" difference between the shortest and longest.
Hope this helps.
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Raydar
From the Department of Redundancy Department.