i listened to the knock with headphones. if you're talking about the sound that's like a diesel slightly clattering at idle, then i heard it. do you have forged pistons? if so, they're set-up with a little more clearance than cast pistons. if it disappears after fully warm, it's probably just piston slap like fmos said. i had a 302 that did this with forged pistons, except louder than yours at startup and was quiet when warm. if you have cast pistons, it still could be piston slap that should disappear when warm. the coolant leaks are probably coming from a gasket that's deteriorated while sitting stagnant for so long. you should be able to visually see the coolant coming out of the engine when idling, at that rate of leakage, if you can see the area (look around with a flashlight, small inspection mirror, etc.) check your oil to see if it's got water in it just to be safe. just some ideas.