That is a Centex checkvalve - an aftermarket add. Checked mine yesterday and there is nothing on the gen exhaust hose. What is your reason for changing the muffler to a 10" model? looks like a few others have gone this route as well.
I switched out the factory 6” dinky muffler on my 400DB. I called Centek and they recommended their 9” dual stage muffler part number 1529001. So I bought it. Good news it was plug and play install. I didn’t even need to cut down the top hose. A fellow CSR 400DB owner, My3sons, replaced his at the same time and went with the 10” single stage. He had to do some minor work to fit it in. We’ve compared sound reduction and hard to tell which one is quieter. But there definitely is more water sound and less exhaust sound coming out of the hole. But, the rata-tat-tat of the motor through the cockpit floor is still the driving noise you hear. Muffler doesn’t do anything for that. The 10” was half the price of the dual stage. $200 vs. $400.
If you check out the newer 52DB the cockpit seat seems to also be recessed into the transom area thats a pretty smart move by SR to gain more space in the cockpit. I would look at this before moving the whole transom. You would lose all your transom storage however. Still seems like a lot of work though. Maybe cheaper to just get a different boat.
How do you carry your tender? I don’t see a lift and am still trying to decide which system to useInteresting idea. Seems like a big job to get it right and properly integrated with the aft corners and transom door. Probably would require modifying the transom module to match the contours. The obvious location would be to match the port side contour aft of the shower hatch. You would need to manufacture a new door to look right. Not sure if that location would avoid being on top of the swim platform ladder. There is a fair amount of electrical that may need to be rerun as well.
The obvious Pro is more cockpit space, as you mentioned.
Cons: A lot of effort to gain I am guessing ~8" of space unless you make really big changes (even more effort), integrated swim platform may look strange, necessitates an extended swim platform (looks like you already have one), potentially awkward access when swim platform lowered, impact on resale unclear.
I think I would maybe get a bigger boat!
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