The 3 port pairs are only similar, not identical.
The intake differences:
1-2 has 240° 480° 240° firing order separation
3-4 has an even 360° 360° interval
5-6 is 480° 240°; the same irregular interval as 1-2 but with the inner/outer sequence reversed
The exhaust differences:
1 is an individual port with a 720° rotation
2-3 has 240° 480° 240° firing order separation
4-5 is 480° 240°; the same irregular interval as 2-3 but with the inner/outer sequence reversed
6 is an individual port with a 720° rotation
This will be very complicated with minimal results, L6 siamese engines have been popular for over 100 years.
