My opinion is that black smoke is an indication of improper fuel/air mixture (running rich) and it may just need a fuel/air mix adjustment. What kind of mpg are you getting? I'll ask this question but I think blue smoke is burning oil - What is the oil consumption like? If it is using more than a qt of oil in 3000 miles it may just need a head job - valve guides and seals. Or maybe you need to add a bottle of Chevron Techron and take the car out on the freeway and run it up to redline a couple/few times and then follow it while driven easy to see if it is still there. How do the plugs look? If it is running good I would not even consider a bottem end rebuild but if you pull the head I would recommend changing the timing chain, tensioner and guides.