Oddball stroker question

I'm a life long Mopar guy and a life long boat guy. I have been boat less for about 12 years, and that is changing at the end of this month. I am picking up a 1973 27' Magnum Marine sedan that is powered by twin small block Chrysler marine engines. I'm not sure yet if they are 318s or 340s. They were dressed the same from the factory so I wont know until I get the boat and check the block numbers. Anyway my plan is to build a pair of 402s out of 360 magnum blocks to get me the Hydraulic roller cams. I am going to add a closed cooling system so I can run an aluminum intake, and I'm on the fence about RHS Iron or Eddy Aluminum heads. My question is do I NEED to run the Forged Scat crank or is the Cast one going to be enough? I'm keeping the compression low, around 9 to one so I can run the 87 Octane at the marina pumps. The motors will never see over 4600 RPM, but will see 42-4400 RPM WOT for long periods of time.

Engine compartment:
http://s184.photobucket.com/user/murfman_photo/media/image_zps3a3180ba.jpg.html

Thanks to some guys down under the restrictive Log manifods can be replace with these:
http://s184.photobucket.com/user/murfman_photo/media/IMGP1781-croppoed_zps961e1e4f.jpg.html

The boat:
http://s184.photobucket.com/user/mu...b-4cc2-8a28-3d1040082a80_zps3a3db728.jpg.html

For people that don't know the Magnum, it was built by Don Aronow the guy that started Donzi, Formula, Cigarette. He had a huge hand in creating the Offshore racing scene. The US Coast Guard has used the 27 Sedan as a patrol boat and they were in service for over 45 years, they were also the boat of choice for the Kuwaiti Coast Guard. With twin 400 HP motors I should be able to get 70 MPH from her and she is a Wave Crusher.

http://s184.photobucket.com/user/murfman_photo/media/PRESSECA_zps8fc086d8.jpg.html

http://s184.photobucket.com/user/mu...1984-Kuwait-Patrol-Boats_zps7896f9f4.jpg.html