Sounds like you are doing this work for all the right reasons. As RAC said, you might be able to get the current ones moving, which solves part of the problem. You would still need to correct all the plumbing, as you pointed out. That may turn out to be the main issue if you can get the sea valves to open and close. You may not need to replace them.
If you look at some of RACs posts on his engine room, you will get an idea of the quality of work he expects from himself and on his boat. I would feel safe taking his suggestions.
The best source I have found for this kind of hardware is Groco here in MD. (now, part of this is that they are local to me and they make everything here in the USA, although their actual foundry is in PA- but it isn't overseas) Their ARG series strainers are very good. I have several of them and they are very good about keeping spares and gaskets etc for all their products, old and new, in stock. I have a Groco FW system pump, for example, that probably has fifteen years on it, now.
Jim, thanks for the kind words. Let me address the post and your PM together here.
First, freeing a stuck seacock won't be fast. But it is a lot cheaper than replacements.
Spray penetrating oil on the valve assembly copiously and often--maybe every time you pass by for days. Also spray oil on the freeze/drain plug. Also, disconnect the hose from the seacock to the pump at the pump. Stuff a rag down the hose until you feel it at the seacock. Pour in full concentrate phosphoric acid or CLR. The rag helps stem the flow of the acid out the open seacock. Let this stand, and continually refresh solution. Continue oiling valve assembly. As an alternative, a diver can remove the screen and stuff the intake which is a good route. But you may not be able to fully close the seacock until the intake is cleared.
If necessary, make a cheater about a foot in length. Being careful not to round off the valve stem, work the handle back and forth. It may not move for the first few tries (or days). But, most of what you're doing doesn't take much time at any one session. Use a brass hammer and whack the assembly pretty good at anytime during the process. I thought an orbital sandy was a useful tool on helping to free things up.
After a time, the seacock will move back and forth a bit. Don't trying force it. Using a coat hanger, pull the rag out. Now, you can use a torch and heat the seacock. It's pretty massive, so you shouldn't worry about melting your boat. Work the heat all around the body; it'll take a while. Go the whip (hammer). You can wet the base of the seacock and watch for signs of heat rapidly evaporating the moisture as a safety check. Re-oil when it cools down.
Once the seacock is about halfway closed, remove the freeze plug and screw in a zerk fitting. Shoot some grease in the assembly. Most of the grease will go in the water until the seacock is completely closed. Then, grease it well.
Also, once the seacock is closed, add CLR or about a 50/50 mix of phosphoric and let stand overnight. I think you will be surprised at how easy the valve will open and close after a day or two. Exercise regularly and it should become lighter and lighter to the touch.
Seems like a lot of work, but it's really just a couple of hours total spread over time. Good luck.
