I disagree with the need for a roller cam. A good flat tappet cam will outlast cheap rollers any day. If you want good mid-range to high-range rpm power, start with a good single plane intake. The single plane will require a bigger accelerator pump shot, so you'll have to adjust the carb. Better yet go to a 750-850cfm carb. Headers next. A mild cam (what we used to call a 3/4 race cam) will really wake up the intake and exhaust. Make sure you have a nice hot spark, either a late model electronic or MSD. You can make a lot more power with these items before you have to spend money on heads and roller cams.