For those following here is what I'm going to attempt:
-Two of these:
https://www.hardin-marine.com/p-7394...per-brass.aspx
-A two-stage water pump

1. Raw water enters boat / strainer / water pump
2. Raw water exits one stage of the water pump and enters Heat Exchanger 1
3. Raw water exits Heat Exchanger 1 and enters oil & power steering cooler combo
4. Raw water exits oil & power steering cooler combo and enters exhaust on one side
5. Raw water exits out exhaust

Then on Heat Exchanger 2:

1. Raw water exits the other stage of the water pump and enters Heat Exchanger 2
2. Raw water exits Heat Exchanger 2 and enters the exhaust on the other side

Heat Exchanger 1 & 2 will be mounted on top or next to each other outside of stringers.

1. Thermostat opens and coolant exits engine, entering Heat Exchanger 1 inlet
2. Heat Exchanger 1 outlet is connected to Heat Exchanger 2 inlet; coolant goes from Heat Exchanger 1 to Heat Exchanger 2
3. Coolant exits Heat Exchanger 2 and enters engine circulating pump

Those Hardin heat exchangers have 2 raw water outlets that are supposed to go one to each exhaust - I expect I will plug one on each, since each of my heat exchangers will only empty to one side exhaust each (assuming this makes technical sense)

The purpose of the above with a two-stage pump is to get equal temperature water into each heat exchanger for better efficiency, rather than having warmed up water exit one and enter the next.

Any thoughts on if I should have the raw water go to the oil & power steering cooler first instead of the engine heat exchanger?

Did you speak with BAM?.....interesting enough, he has a set of engine heat exchangers, brackets, tanks for both of his 1,000 plus hp engines that he fabricated quite a few years ago for his Cigarette.

All that seems like way more trouble than it`s worth and $$$$$$!!

MR. Cool will make you any cooler you want , quick and very reasonable.

https://www.mrcool.us/

$4k is a big chunk of change for the 2x BBC exchangers. Plus the mounting costs etc.

Dan mentioned Mr. COOL.

https://www.mrcool.us/coolers/univer...xchangers.html

They have some universal exchangers that don't have expansion tanks attached to them. So you can set up an expansion tank in a convenient location.

They may even make you a custom setup. Or a single. They should be able to place the outlets where you want them.

^^^^ agree 100%

They made me some custom fuel coolers in like 2 days and extremely resonable.

+3 For https://www.mrcool.us/

Thanks all. I ended up getting in touch with Marc at BAM and bought his heat exchangers. I did call Mr. Cool but they weren't able to make anything for 1000hp+ - I think the highest they said they could do was like 800hp? They do have a 1000hp oil cooler option though. Their sales guy was very nice.

For anyone who stumbles on this thread I did buy both of the BAM heat exchangers in a package together, but I only need one if someone is looking. Will edit this or post again if someone ends up buying the other from me one day.

Thanks again for everyone's help and advice! Will let you all know how it goes.