Unless your cam is big enough that it has a distinct lope at idle, a stock convertor may be less than ideal, but it wont make the engine stall when you put it in gear. It sounds like you just have a minor carb tuning issue, possibly combined with timing. My 302 has a cam with about 280* adv duration (220@050) and it worked just fine with a stock convertor, no stalling. My advice would be to drive the car around to get it fully warmed up, then set the timing to 12* with any vacuum advance disconnected. Then turn the idle mixture screws in and out until you get the highest rpm. You can use a low rpm tach to help you get the highest idle speed, or the highest reading on a vacuum gauge will achieve the same result. Then use the idle speed screw to set final idle speed to around 850 or so in park/neutral. Ideally, both mixture screws should be roughly the same number of turns out when youre done. It may just be common sense, but of course make sure that the choke is fully open and not flopping around, and that the carb doesnt have any leaks wether internal or external.
