I'm still digging, but you may have to make your own elbows so you can fit them to the available space in your bilge. You would have to use something like this ebay tubing provider:

http://www.ebay.com/itm/5-409-Stainl...01005413598%26

and this one, (both may have 4' and 5"):

http://www.ebay.com/itm/Flowmaster-M...63ba6b&vxp=mtr

So, to manufacturer your own elbow. You'd put a 4" that was longer inside a 5" and weld the ends closed to make the jacketed elbow. It would have to be the correct inside diameter on the one end to slip over the current header, and weld the studs on for the strap attachments. Plus a water inlet so the water could come out the header like now but go immediately into the elboe inlet. There would be holes inside the 4" inner tube on the outlet end to let all of the water go into the exhaust so it would be wet the rest of the way. You could probably shorten your existing tees to use, and everything would be held together with 4" ID exhaust hose and stainless hose clamps. That way your elbow would be cooled by the water in the jacket, which would continue inside your exhaust the rest of the way.

I'll think about it more, but it may be the only way. As the others think about it and put in their input, plus others review and comment, we should be able to sketch up a workable plan that can be quoted.