The ignition itself draws very little power. So if you don't have electric fans, big amp sound system etc. it should be fine. If you're already border line it's possible the HEI could push you over the edge.
Shouldn't be a problem. Just keep in mind, the alternator's job is to keep the battery "topped off" so your car will keep starting and running. If you consume more power from the battery than can be "replaced" by the alternator's output, you will eventually drain the battery and the car won't start or run very long.
So the answer to your question is dependent upon how much other "stuff" you are draining the battery with. If you are like my brother and try to power a bunch of non-automotive junk too, no, the alternator won't power the HEI distributor and a TV, stove and refrigerator at the same time. You'd have to refrain from cooking while driving or install a larger alternator.
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