If you take the springs and weights out of the distributer then you need to keep it from moving..lock it out, otherwise your timing will be all over the place. If this is a factory HEI then 3000 most likely isn't enough, but if you lock it out you can set it as low as you can read it accuratly. Plugs can be black for various reasons like rich idle mixture, too much jet..
Are your valve covers baffeled?