replacing thermostat on Indmar 5.7L; which gasket do i need?

[srab]

2006 boat with 320 LCR, but Monsoon should be the same.

Bakes shows two different gaskets.

Which do I need, or do I need them both?

Thanks.

[mackie12]

that housing should be a two piece I believe....only need the bottom one....

[srab]

UPDATE:  Finally made it out to the boat today (lives on a lift at a covered marina).  Had the new thermostat and the two-holed lower gasket, but was stymied! 

On this engine, again, a 2006 320 LCR (though I'd think the Monsoon would be the same), the thermostat sits between the upper and lower segments of the housing. 

So, should this question ever arise again, the 3 bolt gasket is the must have gasket when changing the thermostat. 

IMHO, though, you should probably plan on replacing both gaskets.  After removing all three bolts, it may be possible to pry open only the upper portion of the housing without disturbing the seal on the lower housing, but it is probably more likely that you won't, in which case you would need the lower 2 bolt gasket as well.