Since you are looking for an H1C water cooled turbo I assume this is a marine application. One turbo part number was originally 3522900 which later was replaced by 3523244 and is now part number 3528745. It is quite possible there are other numbers too. I believe the 4bt and 6bt marine engines used the same unit but I'm not positive on that . A Cummins marine dealer could tell you the exact unit for your engine. If you have an engine serial number I might can look it up on Cummins Quick Serve for you just to be sure. You can find those turbos on Amazon, ebay, and from many other dealers. They vary widely in price. Have seen $600, $1400, and a lot more depending on the source. That $600 unit is not a genuine Holset turbo and may not be equal in quality to the real units. I've seen a good many of the genuine units in the $2000+ range.