Get the easy to take out Merc Blue Block drain plug set-up and drain your water when put back on the trailer/lift/etc. Makes even aluminum heads last longer. I suppose even better to drain when engine + water still hot.

Yep, I also learned the hard way about re-using head bolts. Had a set of ARP's in my 454 that I tried to re-use. They had been in the motor for several years, but looked fine - no corrosion on the threads. Ended up snapping one when torquing them down.

Would you suggest doing that even in fresh water?

I this the original 20 year old block? My buddy had an issue with a thin deck from salt use after a dozen years. The deck itself had corroded to the point of only supporting a few threads. He was religious about fluk.shing / saltaway, etc. Something to look at if its your original 454 bloc

I do it with non anodized aluminum heads and/or intakes. I am on a drinking water (that fresh !) lake and you'd be amazed how non treated aluminum get's eatin'.

I've just owned single engine boats so real easy to drain the blocks. 2 plastic o-ringed wing nuts that are installed finger tight and wallah.

All Cast iron engines live forever here. You have to freeze them to break them.

#5 + #6 in pic below:
Link here, which you can get any Merc dealer of course:
http://www.mercruiserparts.com/Show_...K+AND+CAMSHAFT

Make sure to get a few extra of the #6 plastic wingnuts. Since plastic easy to brake especially if over tightened. Again, oring seal, so you don't tighten down hard at all. Don't remove and tip down, oring may fall off.

Simple !

I have seen the ARP head bolts and studs, corrode in the cast iron block, especially with non blind bolt holes. I think; they corrode just due to the simple fact; dissimilar metals. Pulling the threads is not uncommon in a block that has open holes to water jackets. I have seen ; someone else strip out the threads in a new Dart block. How they did it ;I have no idea.
Even if you boat in fresh water, upper Chesapeake, brackish water I would still flush my engines with a neutralizer (salt away). The mineral content, in fresh water will cause issues also.

even if useing new top quality bolts the threads in the old blocks can strip out.every time a bolt is torqued in the open holes the threads get a little weaker.the decks on the older blocks were not real thick to begin with and if resurfaced several times through the years it sure does not help the situation.the main reason racers use studs instead if bolts is the studs stay in the block and the threading is done with the nut.

i usually run a tap through the holes first and se how they clean up..it i see any threads missing i will install a keysert..they seem to work the best... http://www.rivetsonline.com/thread-r...keenserts.html