I agree with Bill.
When we bring the exhaust manifolds into the Closed Cooling System loop, many things change.
Couple of things first, if you don't mind:
I'm not sure what you are calling a "hooker", so perhaps you could explain.
When you say "tank" are you referring to the Heat Exchanger?
And perhaps explain "two tanks per engine".
When we bring the exhaust into the "closed cooling system" loop, the Heat Exchanger capacity must be increased.
The sea water pump capacity is typically increased also.
I know that BTUs are BTUs, and you'd think that this would be Apples/Apples, but the smaller capacity H/E's for a "Half System" will usually NOT work for a full system..... nor will the smaller sea water pumps.
The thermostat housing changes significantly as well.
Likewise do the coolant return inlets on the H/E.
The risers are also now blocked off from the manifolds completely..... and become fed by the "spent" sea water that leaves the sea water side of the H/E's tube bundle.
What I'm saying is.... the complete system needs to be set up correctly for a Full System, if that's what you want to do.
I'm afraid that you'll chase your tail if you attempt to convert or adapt a half system as to include the exhaust manifolds.
Probably not what you wanted to hear! Sorry!