Basically you have two sets of (original) exhausts, fore the 3ma1 and 3ma3
They are about the same, but with one big difference
(Top pipe is 3ma3)
A 3ma3 pipe has a slim slow angular diffuser compared with a 3ma1 pipe.
So a small conclusion
Internal diameter tailpipe is a relative good, compared with modern pipes.
23mm is proven to be correct.