I have a 3.0 but it doesn't have any tubes like yours. There is a single blue plug down on the block though, under exhaust manifold. There are also brass plugs on top and bottom of exhaust manifold, and on thermostat housing. Last year I opened them all, poured in RV antifreeze until it came out each and closed them as it did (made sure it flowed full antifreeze, not mixed with water). I also only boat in fresh water so flushing not a problem.
Also before winter I took to changing outboard gear oil, and engine oil and filter.
BUT BEFORE ALL THAT, fogging the engine to a stall...
1997 1700SR "MaKs RAT attack"