A few details I noticed on the rear muffler on my 327 car.
Painted semigloss black.
Has the letters 'BAM SP' written on the top side with a white marker pen.
Part number 2809468 stamped on the lower passenger side.
Also has the letters S 4 77

I've got a 1978 Repco exhaust parts manual and it lists different part numbers 7449073 for HK327 rear muffler, and 2809468 for HT350/308/253 rear muffler.
So thats 10-years later and the part numbers were still different.

According to the Repco drawings the HK327 muffler inlet pipes were flared to accept the intermediate pipes, while the HT/G muffler wasnt flared but the intermediate pipes were.
Maybe that was the difference?
Anyway thats Repco.