77KZ750 Mufflers

I have a 77 KZ750 and have a question. I am wondering what this exhaust is. I bought this from the original owner and he said these were added in the first month he owned it. It is all original except the seat and tires. I do have the seat in storage for a back up. But anyway if you can help on these mufflers please do. I am thinking about something more modern or performance oriented. I am sure these are better than the stock ones but are still a small outlet hole and think something bigger would breathe better. I like a deep tone and these are a little cracky for my taste. Any suggestions would be welcome I can not get this picture to load please help or let me know where to send them

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