1975 318 Y pipe vs 1974 318 Y pipe

I thought I read on here that the 1975 and up Y pipe for the catalytic converter has a bigger passenger side flange that bolts up to the exhaust manifold vs the 1974 and down Y pipe without the converter. If anyone knows for sure please let me know. This Y pipe that I bought had the set up for a converter and that might explain why I have a small exhaust leak coming from the passenger side flange.
Thanks
Bob