Difficult question to answer. Different species of conures will have different average weights, and that again is just an average. Best advice I can give is to have your avian vet do a wellness check with a physical exam to determine if he's at a healthy weight. That establishes a baseline for comparison. Moving forward from there, regular weight checks are a very helpful tool to alert you to health changes that you might otherwise not notice.
74g doesn't sound out of the question for a conure, but they're all individuals. Of course, that sounds tiny to me since my birds are larger. My YNA is a consistent 650, give or take a few grams, and my Ekkie is stable at 420-425. A 5 gram difference for mine could simply be a matter of when they pooped last, where 5 grams to a 74 gram conure is a substantial change, worthy of concern.