brass water pump impeller housing

That is a Volvo-Penta impeller housing. The one posted is an old style, that used plastic tubes with o-ring seals. If you look inside the ports, you will see that they are machined smooth for the o-ring seals. The plastic tubes and o-rings were prone to leakage, so the housing was redesigned with the long bronze tubes, to eliminate the plastic and o-rings. The first 2 links show that pump with the plastic tubes. The 3rd link shows this pump that has been rebuilt, with the plastic tubes being replaced with copper. There a mention in the 3rd link, under Product Description, about the plastic tubes being replaced with copper.

References:

https://www.ebay.co.uk/itm/286216520544

https://www.ebay.com/itm/256688284666

https://rawpumps.com/products/volvo-penta-raw-water-sea-pump-rebuilt-21427730...