adding more chain will make it more challenging by hand. Chain is tough on your skin and when it comes to weight you'll get much more holding power if you put the extra weight into an oversize anchor rather than more chain. I'd keep the short chain simply as chafe resistance from the bottom, and consider a larger Danforth or even larger Fortress. An FX22 would be plenty large on your boat and only weighs 22 pounds.

Also, if you cut off your old rusty chain, your rode's life might be extended if you swap active ends and splice in new chain. I also recycle the tail ends of old rodes as bridles (which I change every two years or so). They don't see much wear from sitting in the bottom of the locker, and they're a little harder to splice but workable. If they're really hard you can soak the salt out in the bathtub a few times or hit them with a power washer along the whole length to get the crust and dirt off, then let them dry out before splicing.