[Day2_69Z]

This is the proper end crimping on NC8 pipes, the front intermediate pipes have the same crimped ends.
The deep crimpings are also seen on the center crimps.
These are 27 year old C&C reproductions done from original GM pipes & blue prints.
I believe the current value of such sets range in the $3,000-$4,000 area.

The Gardner pipes Do Not have the end crimpings nor the Deep 4 pronged crimps on any of there pipes.
IMO ,the Gardner Chambered exh. looks Quite generic and a low level attempt.

Another source is to look at any of your ERTL 1/18 Diecast 69 Camaros....look at the pipes.
MONOGRAM MODELS in the 80,s used GM Blueprints & 3 Original NC8 CARS to scale there 1/25 scale 69 Z/28 ,YENKO, PACE CAR & Baldwin-Motion models to exacting standards.