reusing the old block is fine as long as you have it inspected before you have all the work done to it. it would suck to put money into a block thats no good, but chances are that its fine cause its running now. i was reading some of your past posts and i noticed that you said that you had been moving the idle screw in and out, have you been adjusting the tsp voltage as well? if not, that could be a big problem. see any time you move the idle screw, you have to adjust the tsp voltage with it. the voltage should be .98 vdc. if your not sure what im talking about, let me know and i'll explain it or you can do a search for it, its pretty common.