Some early Pearson Yachts and Allbergs had no seacocks on the cockpit scupper drains. They had fiberglass pipes on the hull with no seacocks! My 323 has an Atomic Four and the same Wilcox Crittenden tapered plug seacocks you have but they are mounted further towards the stern. I'm able to loosen the tapered plugs and clean and lube them but I am also restricted from complete dissembly from within the engine space. I had them out of the boat when I first got ALMA 12 years ago because they were seized open. At that time I had a marina remove and restore them for me. Now I am able to keep them operating and leak free by greasing them in place. I haven't needed to take them out of the boat again. It looks from your photo you may be able to do the same. If they leak- just removing the plug's nuts and slipping sandpaper between the plug and housing to lap them next haul-out should do the trick for you. Be sure to rinse them very well after the sandpaper treatment. Removing the hose and it's barbed fitting helps. You can find the rubber washers at a good plumbing supply. The original W-C washers were
leather. Remember to buy spare washers! I think it would be more difficult to clean grinding paste from them than sandpaper grit. I've had good luck with the 320 grit sandpaper taking the contour of the tapered plug and it's seat. If they are seized and won't come apart you'll need to R&R them next haulout. You may read about using a hammer and hard wood to separate the cone from the housing. You risk destroying the cone doing this. 'Better to use patience and PB Blaster or heat. A heat gun is superior to a torch. If the housings are installed in the boat don't heat them. Once they are refurbished your annual maintenance will keep them working well. When my boat was made all the underwater metal was bronze. I never wanted to introduce a ball valve because of it's stainless parts and corrosion issues. Now I have a stainless prop shaft so the introduction of a stainless ball valve isn't so important. If you are lucky enough to still have all bronze underwater equipment it's worthwile to try to keep it that way. Once you introduce stainless you'll be setting up a galvanic cell. If you have stainless prop components or shaft already...ball valves would be a convenient replacement. I wouldn't call them an upgrade. Ball valves are not as durable as the W-C valves and are popular because they are cheaper.
This link has a lot of good info about tapered cone seacocks. http://www.pbase.com/mainecruising/tapered_cone_seacocks