NOS Transverse Dual Exhaust1969 Camaro Muffler 302 359 396

[1969camarors427]

I have a NOS Muffler that I am trying to find some information on.
The part number on the box is #743538
The only information I can find on this part number is a post from 2006 by Jonesy on the Camaro.net site who I think is also a member here.
He posted the muffler part #3981951 then became part #743538 - Muffler (tranverse) on a reply to do with 1969 Camaro 396 exhaust part numbers.
If anyone has a part number change-up manual that can check for me would be appreciated.
The box is dated 6-78.
Thanks for any help. George