I am in the process of installing Holley 250 superchargers on my carburated 502 mag engines and am perplexed by the water pump issue. The new blower manifolds do not have the same type of setup for the factory thermostat housing. If I keep the original water pump on the front of the engine, where do Iplumb those gigantic hoses? And, if I go with a crossover pipe, how does that plumbing go together? Does anyone have a BASIC diagram of how these hoses should look for both setups with roots style superchargers? Any suggestions are appreciated!! Bob

Use the Stainless Marine crossovers. They have the specific port lengths to run from intake to block.

I have B&M 250's on my boat, and run the stock reculating pump on the front of the engine. I boat in colder water, and maintaining engine temp is important up here. How it is run is I use the B&M / Holley water neck, I believe it is part number 155160 for the 250's. It is a water neck extension, and at the top of it you mount your thermostat housing, so you can run your thermostat the 1 1/4" water supply hose and the 1" hose to your headers.
I don't see this set up very often, but I really like it. If boat in colder water temp, and you could find these water necks I would highly recommend them.
Sorry I don't have any pictures. The boat is put a way for the winter, so I can't get to it.
Good luck.

Thanks for the advice. I am running stock outdrives with a standard sea pump so high water pressure should not be a problem. So the gigantic hose that exits the stock water pump on the front of the engine connects to the thermostat housing? I ordered what I think is the thermostat housing part you describe. One end is very long. It connects to the intake.

No It sounds like the part you are talking about is a stainless water neck. You use that in conjunction with a crossover.
If you want to keep the recirc. pump on the engine you need to try to find one of the water neck extensions I mentioned in the other post. I don't see them very often, but they should be out there. I looked in the Holley marine catalog and they list the part 155160 as a 90 degree thermostat housing for 250 power charger.
I know a lot of guy's like to take the recirc pumps off and run cross overs, but Merc ran recirc pumps on the old 525SC and the 600SC'sc with the B&M 420 blowers.