Again just conversation but what's the actual goal here?
Example a ford crate 347 is rated 415 horsepower but if you're pushing that through this thing
you're probably making like... maybe 350 or less? If you bolt on a supercharger that just means stuffing even more sausage through that casing.. every molecule of fuel you burn plus its accompanying oxygen and nitrogen have to get pushed down an already crowded hallway.
To be clear I like catalytic converters. All of my cars have them despite no practical need for me to remain compliant. But that midpipe is like 2.25" tube and those four cats probably aren't particularly high-flow compared with modern ones. I had the luxury of buying an aftermarket midpipe with cats and it was noticeable on a mild 302.
If that piece of metal is unavoidably part of your equation due to local regulations I just don't see how devoting any more effort to peak horsepower is going to do you a bit of good.
I'd be optimizing the car in other ways - or - buying factory built horsepower that doesn't need any fiddling to go fast or pass emissions.