Thermostat location

I have two CH 350 454 engines, vintage 1979 SN about 65000, these engines have the engine cooling system that recirculates engine coolant thru the complete exhaust manifold with the blockoff at the rear of the exhaust manifold just before the riser,(which is salt water cooled).
My question is, What is the correct location for the engine thermostat? I don't know if they should go,
A. Between the Manifold and the spacer that has the Temp sending unit?
B. Between the Temp sending unit spacer and the lower Thermostat housing? (both the coolant hose pipes are blocked with factory rubber caps) and is the style that was used for raw water cooling but doesn't use the popoff valve.
C. Between the lower Thermostat housing and the Top cover that has the hoses that connect to the front of the exhaust manifold?
I have looked everywhere for a picture or diagram with no luck.
Thanks for any help

serial numbers that high are NOT from 79.

going on the serial number being more accurate that the date given, the thermostat goes in the thermostat housing. Go here and scroll down to find the FWC thermostat housing - newer diagram:

http://marineengineparts.com/shopsite_sc/store/html/page552.html

Just one comment on that 3 piece thermo housing system. You can buy one new casting and get rid of those rubber caps. I did have one cap blow out on me years ago. That change will remove a bunch of failure points from your engines.

Thanks guys for your advice and the link.I put the thermostats in the correct spot and now the temp acts correctly. Just one more question, if i change to the new style housing how does the coolant for the exhaust manifold get to the manifold before the thermostat opens?
By the way, Mark you were right about the serial #s the actual number is 25950 on the starboard engine, dont know where I came up with the other number!

757guy said:

Thanks guys for your advice and the link.I put the thermostats in the correct spot and now the temp acts correctly. Just one more question, if i change to the new style housing how does the coolant for the exhaust manifold get to the manifold before the thermostat opens?

Click to expand...

Of course, the manifolds are always full of coolant. BUt, during warmup I suspect there is very little flow thru the manifolds, and yes, they do warm right up!